<p>What are the benefits of upgrading from Visual Studio 2005 to 2008?</p>

<p>Any thoughts on whether it's worth the jump, or is it better to wait for whatever's coming next?</p>

There are tons of improvements. The best part is you can continue to target .Net 2.0 with VS 2008 (
Multi-Targeting
) and use all the new IDE features.
Posting couple of screencasts but you can find more on web:
Script intellisense and debugging in Visual Studio 2008
Multi-threading Debugging Enhancements in Visual Studio 2008