I'm a very big ReSharper fan. I've always been more than willing to throw more hardware at my machine to make sure that I can get it to run well. There's so many features that make me more productive, I think I'll have to post a top 10 or something like that in the future.
Anyway, after installing Visual Studio 2008 the addin wasn't installed and I've been having some withdrawal. I had run across an article that had mentioned there was an early RC of ReSharper 3.1 out there that would work. I found it here.
You have to uninstall any previous versions of ReSharper prior to installing this pre-release version.
After installing the RC, I have ReSharper again.
Now, you won't see any support for the new C# 3.0 compiler features (Lambda Expressions, Extension Methods, etc...) until ReSharper 4. The product manager of ReSharper goes into more detail here, and according to him it looks like JetBrains is shooting to drop that in January.