Based on everything we have read in these postings, we definitely want to go to Plitvice. Would you recommend that we go from Piran or from Trogir, since we will be staying in both places? Also, what accommodations would you recommend in Plitvice? Do we need to book them ahead? (We will be there in September.)
To stay in Plitvice for two nights, we will either have to cut out Hvar or Korcula....which would you recommend cutting? Thanks...........

I wouldn't recommend staying two nights in Pitlivce. One day will do it. In fact, you can walk the length of the gorge and have lunch along the lake in about 3 hours, iirc. We did it as a day trip from Zagreb.

Do go to Hvar.

I am assuming you are renting a car, in which case http://www.viamichelin.com is invaluable for route planning--it looks like about a 4 hour drive from Piran to Plitvice, so if you are staying overnight, I would go there from Piran and then on to Trogir (which I believe would take about the same amount of driving time).
You probably do not need to book for September, there is private lodging near the park as well as a few hotels right in the park. I thought it was most convenient to stay in the Hotel Plitvice. How long you stay depends on how much you want to drive in a day and how much time you want to spend in the park. It is breathtaking!
Hvar and Korcula are both beautiful islands with beautiful towns--it's a toss-up in my opinion.

Dear Ackislander and Yokshire, Thanks so much for your responses. We do have a car, Still not sure what we'll do. The answer should have been to allot more time for our trip. Thanks again.

how do we get t o plitvice lakes from zagreb.any daily tours or tour busses?

We were there last fall and stayed at the Hotel Jezero which we had heard was the nicest of the hotels in the park. It is a bit impersonal because they get all these big tour buses coming in but it was a great location. Do not stay outside of the park. It is not convenient. There is a really good restaurant a short distance from the Jezero (they can give you the name of it at the hotel). And I agree with the earlier posting. You only need one full day to explore the park. In fact, it rained in the morning so we weren't able to get out until around 1:30 but saw nearly all of the park (we are good walkers/hikers) by closing. It is a most spectacular spot. Enjoy!

We stayed outside of the park and enjoyed it immensely more than if we had stayed at the impersonal hotels inside the park. If you have a car, it's really not that inconvenient. And much cheaper. Either way you'll be fine.

What's your total itinerary? Are you not going south of Korcula? If you aren't going to Dubrovnik, Maybe just focus on Hvar. I agree it's a toss-up, although I personally enjoyed Korcula more.

We, too, stayed outside the park as we wanted to avoid the impersonal touristy hotels. We stayed in a small and very charming B&B instead and loved it. You only need a day at the park, anyway, so driving to the entrance should not be an issue.

what hiking trails are the best in the park? we love to walk and are in good shape. are there any websites that show the specific trails, so that we can plan ahead. We have two days in Plitvice.

The national Park website has interactive maps:
http://www.np-plitvicka-jezera.hr/
There is the main part of the park that is most visited (primarily consisting of boardwalks over the lakes, but some trails also), then there is the wilderness area at large which also has trails. A waiter offerred to give us a tour of his favorite parts of this wider region of the park, but the weather turned and we moved on.