There is alot of beta software out there. Google release alot of web applications as beta for years, Silverlight 2.0 is beta, you can get beta (or earlier) copies of Window and more. One thing that people have to be aware of beta software is that it is not complete and you risk things by using them. Microsoft just released a beta 1 for SP1 for the new .NET 3.5 and Visual Studio. Microsoft is saying that this service pack fro .NET will help speed things up and make installers smaller to name a few things. The problem is that beta software could cause you problems if you use it.
It This article on The Register give a clue to the latest issues with people that play the beta software game. So having the beta version of Silverlight and the beta version of .NET 3.5 will make it so that you could have an error installing the SP1 beta or make it where you cannot do your Silverlight development. Scott Guthrie says that they will be putting out new Silverlight tools in the next few weeks to help with this.
I limit the amount of beta software that I use. I am playing around with Silverlight beta 2.0 and will not be putting the beta of the service pack on my machines. Keep reading this blog... (and Scott's) for more info on this issue.