I've been developing in Visual Studio 2005 (February CTP) for a few weeks now and thought I'd talk about the experience so far.
Installation: Fairly painless on the surface. Unfortunately, after a "successful" installation I found that I could not view Content Pages in Design View. Now, I don't consider not being able to use Design View a deal breaker; however, when I switched to Design View VS2005 would stop accepting keystrokes and became unusable. Obviously, I could just decide to never use Design View, but I didn't feel like that was an acceptable solution. After 12 hours of installation and uninstallation I managed to get it working. I have no idea which variable I switched that caused it to work. The only advice I can give is to uninstall everything that VS2005 installs, and perform a custom install and only install the things you absolutely need. Rebooting between each step seems to help also. I gave this advice to a co-worker and he still got 2 failed installs before he got it to work. If you are concerned about the same problem I'd suggest setting up a Virtual PC before installing and uninstalling repeatedly. Another co-worker installed one time and it worked.
Developing: So far we are only taking advantage of Master Pages and Generics but it's worked out pretty well. The only gotcha I've come across is when you rename a Content Page it will no longer compile. Which shouldn't be a problem because you should probably name your pages Default.aspx, Default2.aspx, Default3.aspx, etc anyway. Mike Ward actually found the solution which is to manually change the Inherits value of the Page directive tag to match the name of the class in the code behind. The refactoring is decent, but not yet as good as ReSharper.
The thing I really like about VS2005 is that I no longer have to declare the controls in the code behind before I can access their values.
Building: Building in VS2005 is painless. The only issue I've run into is when using MSBuild to build a solution that contains a File System Web Site. The references for a File System Web Site are added to a solution file; however, MSBuild doesn't seem to pick the references up and can fail. When you add the reference in VS2005 a Bin folder is created and the referenced project's library is added. However, on a CI machine things can get tricky. I've heard 2 work arounds that are a bit sloppy, but I hear MSBuild beta 2 will fix the issue.