I've been developing my personal website in Silverlight 3 beta as a way to learn the new features. However, today I needed to begin development on a website that will be going live fairly soon. As Silverlight 3 isn't projected to be released until maybe July or August (and it could very well be even later), I was forced to choose Silverlight 2. Unfortunately, you can't develop for Silverlight 2 and Silverlight 3 at the same time on the same box. As I'm opposed to using VM's these days after losing about a year of my life due to slow VM performance in the past, I searched google and was lucky enough to find this article:

http://blogs.msdn.com/amyd/archive/2009/03/18/switching-from-silverlight-3-tools-to-silverlight-2-tools.aspx

It gives you a nice .bat script that will automate most of the process of going between SL2 and SL3 so that you can easily switch between the 2 by clicking a few Next buttons and waiting 1-2 minutes. Problem solved!