Yeah, I know the 2.0 managed stuff is beta, but the CeGui# project uses it, which is why I noticed it. The MDX is going to be replaced by XNA, but from what I've been reading, XNA doesn't actually do everything MDX does yet. It doesn't handle meshs and a bunch of other things. But, it is being replaced.
The annoying part is the "it's beta, you should have guessed!" comments. Yeah, you should program for stable versions, but if you are working on a project that is coming out in two years, you aim for what is going to be stable in two years, not what is now. At least, that is how I thought game and graphics development went.
For CeGui#, it is easy. There is already an XNA renderer being worked on. And for Turf Wars, it won't impact much since I'm using Irrlicht which talks to the DirectX 9 stuff directly. But, its interesting how people respond to finding out its beta, and also how people tell them to just "live with it" or "its your fault for using it."