Ahh... Don't you love the smell of fresh software in the morning?
Yes, this is why I've gone silent for a while on my ADO.NET Data Services topics. We've been hard at work for this Beta, and we hope that you'll give it a try and let us know how it's working for you.
You can find a good list of the changes on the team blog, of course.
Shoot. I removed the comment on this post by accident - my apologies to the poster, please re-post if you'd like further follow-up.
Asking for $metadata and getting a 400 - Bad Request was what the poster was asking about, so here is my first stab at this.
400 would indicate that this isn't a server-side problem; instead, something in the request isn't right - perhaps the URL isn't right (probable) or the charset requested isn't supported (not very probable, as you have to go out of your way to request this).
The first thing to do is take a look at the response and try to determine where the rejection is coming from. I'm posting a link or two now on how to use tools to get to the actual response received. The headers may hint as to who produced this (typically one of http.sys, IIS, ASP.NET, WCF or the service itself).
The body typically will also show some hint: http.sys tends to use very short responses, so does IIS, while ASP.NET tends to include real-deal pages (with formatting and everything) as does WCF (which typically has a distinctive look with a blue bar close to the top of the page).
Let me know if you have further information and I'll try to help troubleshoot this.