Just got back from Lausanne. Flew into Geneva on Tues. nite, train to Lausanne (45 mins) then left Thursday morning. I was staying 5 minutes from the train station at Hotel Angleterre right on the lake. It was my first time in Switzerland and here is my quick impression of Lausanne:

1.) Idyllic and clean (think Hansel and Gretel storybook) with beautiful architecture that is very well maintained
2.) Friendly with a small town feel
3.) Beautiful to walk around the lake on the paved path and just take in the scene
4.) I have never seen so many fit people jogging, not even in Germany

I really think you could do this town in a day very easily. I didn't do the Chocolate train so I can't comment. I imagine Montreux is similar to Lausanne?