Hope to hear from somebody soon!

I'm guessing because you wrote Thun & Lucerne twice that you mean you will stay 2 days in those places? 1 day for both Vevey & Lausanne is just not enough. Perhaps you need to take them out all together and see that area another time. I'd put Gruyeres in instead.

I think that you have a nice sampling for such a short trip.
From Luzern you can ascend Pilatus Mountain and experience small city life in beautiful surroundings.
From Thun (or Brienz), you can visit the Berner Oberland peaks if so inclined, and take in any number of the small villages dotting Lakes Thun and Brienz.
Lugano will start off your Italian influence.
Can't speak to Vevey/Lausanne, but read great things about them!

Are you driving your/friend's car, lease car, or a rental car? If one way rental, I hope you know about the cross border drop-off charge.

I would stay a couple of days in Lucerne and a couple of days in either Intrerlaken or one of the towns in the lower reaches of the BO.

Thun, while very cute, is quite a small town- and IMHO too far to easily do the trip up th eJungfrau - for me the top sight.

Sorry, I thought you meant Fribourg in Switzerland. Since you mean Freiburg in Germany, I'm going to revise my suggestion because Gruyeres is too far out of the way. Vevey/Lausanne are also out of the way.

I'd add Bern. It's near Thun & Lucerne. Plus it's such a lovely city.

I think it would be helpful, to me anyway, to know if you're driving or taking rail. Switzerland has a fantastic rail system.

I'm guessing you want to go to Lugano because it's on the way to Arezzo. Lugano is about 2 hours from Lucerne by car.

I do think you can do Vevey and Lausanne in one day. Take a nice boat ride between the two or rail. Lausanne is more of a city and Vevey is a town. Could be a great day on Lake Geneva. I would recommend, if there's time, that you go to Chateau du Chillon while in this area.

Overall for your Itinerary - I personally would stay in Bern for 3 nights - I love this small, architectually interesting city from which you can do day trips to visit Lake Geneva area (by rail) and can even go to Lucerne for a day.

Then onto the Berner Oberland for the Alps experience - Interlaken is probably easiest for you to stay in. You can do a half day in Thun from there plus funicular, cable car, etc., rides to tops of mountains. Then your last day/night in Lugano.

BTW - If you do stay in Bern, I could recommend the Best Western Bristol. Go on octopus.com for a great rate. This hotel is simple (seems they all are in Switzerland) and just a few blocks from the railroad station, so really easy for traveling around.

Sorry, I see you said you were driving. Possible to do what I suggested by car, if there is parking, of course. Don't know if there are parking garages in Bern, but if so you could park the car there and do side trips by rail or contact your hotel about possibility of day trips by car.

Thank you all for your replies, which are very useful.

Greg, I do know about the drop off fee - in fact we're picking up the car in Amsterdam and doing a longer road trip than I detailed here, and will need it for a week in Arezzo. So we'll pay for the convenience, even if we're not thrilled about it. Thanks for alerting me to it all the same.

kenav, I did investigate staying in Bern but parking does seem a problem. Because of this, we've decided to stay in Spiez for five nights and either train it or drive (prefer train) to Bern and Luzern, and do short car trips to Thun and Vevey. If we find Bern absolutely compelling we can skip Vevey this time and spend two days in Bern.

OOOOHHH, Spiez!
Nice choice.
DO take the short trip to Kandersteg (rail might be the easiest?) to ascend to Oeschinensee by chairlift---a beautiful mountain lake. Just spectacular!