It sort of depends on if Tioga Pass, the eastern exit from Yosemite will be closed or open during your trip. If it's open, it's an amazing drive along the eastern Sierras, past Mono Lake, to Reno. If it's closed (and it's usually closed to Memorial Day, but it all depends on the snow load), then it's a long slog to Lake Tahoe to Reno. If Tioga Pass is closed, I'd recommend Napa Valley- it should be lovely in May or June.

4 nites at Yo. seems long.
Perhaps you might take the 4th day to visit Hetch Hetchy valley (sister valley of yosemite) and the historic and always muched talked about O'Shaunessy dam. We have done this and should be done at least once by every Yo. visitor.
May could see the Tioga pass open to hwy 395 and would be a much more enjoyable trip than the drudge back to SF.
You could visit Virginia City NV as it is enroute (kinda) to Tahoe and a very historic place, or...from 395 in Minden NV. go west and link up to hwy 89 north and go thru lovely Markleeville Cal., right on the way to So.Tahoe. This is another very pretty drive.

We spend 4 nights in Yosemite every few years in the spring. I think 4 nights is a terrific amount of time. But it is a matter of what you like to do. We like to spend a significant amount of time hanging out.

We always stay in the Housekeeping Camp because it is on the river and we can camp without having to bring all the gear - we go with a large group of friends and not everybody likes to sleep on the ground

I can't speak to whether it would be better to stay in the lodge or at Curry though.

Another area you might consider is the gold country north of Yosemite on Hwy 49 (Tuolomne, Amador, El Dorado, Placer Co.). The area has some old gold mining towns (Columbia, Murphy, Coloma) and many beautiful wineries. The winery areas are what the Napa/Sonoma area was about 30 years ago.

Check out the following thread for a discussion on the area---http://www.fodors.com/forums/threadselect.jsp?fid=1

The Yosemite Lodge is OK. It is a typical motelish room.
Curry Village is great. I have stayed in both. Just remember not to leave ANY edible things in your car because of the bears.

Have a great time.

Thanks for you replys.
I've been checking out the reviews of Yosemite accomodations. Lots of negative reviews. We've stayed at the lodges in Zion and Bryce and have found them to be reasonably priced and comfortable, so i'm really surprised about the complaints about Yosemite. At any rate, if we do go to Lake Tahoe, any suggestions about where to stay that would be a little more upscale then the cabin at Yosemite. I'm not too fussy. Pretty location, relaxing and clean would make me happy. Making decisions is not my strong suit.

So. Tahoe has plenty of upper scale lodging if you want to search this on the net, north Tahoe also but not as much and Tahoe city even less.
Carson City NV has some nice lodging.
Make reservations.
The suggestion of gold country is a good one, but remember that hwy 49 is a loooong drive and you should turn east at Placerville on hwy 50 to go to Tahoe, as the drive on to Auburn is even loooonger.

Gosh, Pildredge, you make Hwy 49 sound loooong. It is not that long between Placerville and Auburn. I live near Hwy 49 in El Dorado Co. and take it all the time. DH and I take it to go to Yosemite. Very scenic.

We drove from Auburn to Placerville on Hwy 49 a few weeks ago and it took about an hour (it took that long because we stopped at a winery!) A bit curvy, but very pretty with all the new wineries along the road.

Perhaps, I think people would be unpleasantly surprised by the hills and curves after coming all that way on 49 south of Placerville is what I should have said. Also if venturing to Tahoe, turning East at Placerville makes so much more sense.

You are right, Pildredge. If going to south Lake Tahoe, take Hwy 50 at Placerville. However, if going to north Lake Tahoe (or even Reno) you can continue to Auburn and take I80 or go to south Lake Tahoe and go north along the lake.

Curry Village is extremely rustic. Most people are not prepared for that. We are hearty backpackers, but will never stay in a tent cabin at Curry again. (Too close to other people - it's as if you are sharing a tent with everyone else there). A basic cabin is fine, just rustic. We had a very nice room at Yosemite Lodge which is comparable to lodging at other national parks. The sheer number of visitors to Yosemite is what makes Yosemite feel so different to Zion and Bryce.
The hikes from the valley floor are beautiful, but be prepared for hiking a freeway of other visitors. When this wears you down, drive up to Tuolumne Meadows area and take a lovely hike to someplace like Elizabeth Lake, where you may see only a small handful of people. Also, explore the Hetch Hetchy area - nice hike to waterfall.
Your Lake Tahoe idea and flying out of Reno is a good one, especially if you enjoy the mountains.

If you decide to go to Napa Valley and do not want to drive back to SF for the flight home, check out the Sacramento airport. It is an easy airport to navigate and is only 1 hr 15 min from Napa - much less hassle than SFO.

Thanks for all the responses to my questions. I have a few more.
I booked a cabin at Curry Village without a bath for the last week in May (4 nites). I also booked mid-June 2 nites in the yosemite Lodge and 2 nites in a tent at Curry Village. I really prefer mid-june, and keep checking to see if a cabin opens up or 2 additional nites at the lodge. Which way do you think is the best way to go. We are in our late 50s- we can handle rustic to a point. End of May - too cool? especially Lake Tahoe?

If you prefer mid-June, you might like to take the Yosemite Lodge reservations and continue to see if additional nights open up. We are also in late-50's, and at this point really prefer to have a private bath. But it depends on what is ok with YOU.
Another suggestion: www.evergreenlodge.com
This lodging is just outside the park but very close to Hetch Hetchy. My Australian cousins stayed there in October and really enjoyed it. (I've never seen it).

Good luck with your planning!
You could do 2 nights Yosemite Lodge and 2 nights at the Evergreen.

I would just LOVE to get back to Yosemite in May again. Spent my honeymoon there in mid-May, and we bicycled everywhere. The weather can spike up and be surprising hot for May, but generally it is just beautiful. The waterfalls are at their absolute best then, I think.

Growing up, we used to spend a week every summer in a tent cabin -- granted I was preteen thru teenager, but it was wonderful. As fashion/grooming conscious teens, we spent a fair amount of time strategizing a shower in the communal baths and spent a lot of time in the river otherwise. For the honeymoon, we stayed at Yosemite Lodge. I think you will enjoy both.

As for 4 days being too long -- it depends on whether you like to get out and hike, bicycle, or walk. If you do enjoy being out and about without a car, a week might not be enough. By all means go up to Tuolumne Meadows if you have time and if the road is open.

Now, I am not a fan of Napa. I used to live 1/2 hour away, and did enjoy it before it became so commercial, crowded and (others may disagree here), snooty. Take BarbAnn's advice and visit the wonderful wineries in the Gold Rush area -- El Dorado county, Amador, Placerville. There are also some B&Bs in the area, and there are other things to do as well (tour a gold mine, for example?). It's awesome.