<p>I have read on Stack Overflow some people that have converting to C#2.0 to C#3, but is it really worth it?</p>
<p><strike>I have a project that is done at 75% before going in maintenance phase. I am asking to myself if it is worth it to switch to C#3.0?</strike></p>
<h3>Update:</h3>
<p>The project will have a web interface now so before entering the maintenance phase we have to develop the web part (all was done for internal purposes with Windows Forms). Most parts will be resused (back-end). Most people have said that it wasn't worth it in the past because it was already at 75%... but now do you still think it's not worth it?</p>
<h3>What have been done finally</h3>
<p>Finally since we are continuing the project with the web interface we will update to 3.5 for the new year. Thank you everybody for all your input.</p>

Is there any C# 3.5 feature you want badly at this stage? :)
If it is LINQ, you can give
LINQBridge
a try..
With Studio's multi-targeting and LINQBridge, you'll be able to write local (LINQ to Objects) queries using the full power of the C# 3.0 compiler—and yet your programs will require only Framework 2.0.