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Well, this is a wider problem.
.NET 2.0 has been in BETA for about 10 months. This is NOT much for such a big technology and software. However, is always a risk to develop against a BETA rather than finished software. That's not a .NET thing: that's a common problem. So if you decide to develop against a BETA 2.0 instead of final 1.1 you know you're taking risks and you will probably need to change (hopefully!) small parts of your code when software gets finalized and released.
As a sidenote, the open-source model made it worst. Yes, having sources always available and people developing against snapshots (not even BETAs!) helps developers to find bugs and to customize software to user requests, however that also make a lot of "pollution" which is always bad.
If you look carefully, you will notice ecosystem is full of programs written against partial snapshots, customized versions of software downloaded from other websites (which hold "private" snapshots), buggy versions, BETAs, ALPHAs and so on. It's a mess!
There's a lot of people complaining that their code developed against an early early early ALPHA version of some APIs is not working in BETAs anymore. Or people complain that "they are forced to change code again after I did for switch from ALPHA -> BETA..." (!!).
Microsoft didn't act like that a few years ago and they started spreading almost-complete BETAs only. Now MS has been forced to please developers who are getting accustomed to have code released faster by introducing CTPs, pre-BETA, early-BETA, RC1, RC2, RC-almost-finished and so on. That's not bad as a whole but people should remember that developing against such versions IS a risk.
FYI, I'm developing against WWF and WCF BETAs too but didn't do that until MS allowed GO-LIVE licenses for such products.