I would like to see .NET framework penetration numbers. A lot of .NET developers still target 2.0 for desktop apps because the perception is that that 3.0+ have a much smaller installation base - even though numbers posted on statowl.com and Scott Hanselman's blog suggest otherwise. This is definitely one case where more transparency by Microsoft would benefit both them and the developer community.
I would also like to see the Certificate Revocation List checked less frequently. Microsoft Office add-in developers actually get penalized for having digitally signed add-ins, since the (daily?) CRL check slows Office application startup significantly.
I suspect one of the problems with WPF/Silverlight adoption is the requirement to learn another layout language. I'm working on a rather large Silverlight 4 app, and am generally happy I don't have to work on many UI layouts. I can't muster up the desire to learn another markup language.
I would also like to see the Certificate Revocation List checked less frequently. Microsoft Office add-in developers actually get penalized for having digitally signed add-ins, since the (daily?) CRL check slows Office application startup significantly.