No, I would advise not. I would advise starting 3.5 on new projects only, unless there is a specific reason otherwise. You will not have any benefit from 3.5 by just recompiling, since your code is already written (or at least 75% of it).
If you need to migrate to 3.5 in the future, you can easily do it. Of course, you will have code in 2.0 style, but what is done is done.
- Be conservative, don't do something unless you need it.
- An application which is 75% in C#2.0 and 25% in C#3.0 is not exactly a nice beast to maintain. A 100% C#2.0 application is certainly more maintainable.
When you are going to start a new project, then by all means switch! The new framework version is very interesting and the switch is hotly recommended.
