Yes, xVal is still being developed! You're right that there haven't been any "official" releases since February, but if you check out the "Source code" tab on Codeplex, you'll see that there have been numerous updates since then.
I'm calling it "beta" simply because there are still some features I want to include (culture-sensitive client-side message formatting templates, a dynamic client-side validation summary helper, and possibly Ajax-powered remote validation)
before calling it the 1.0 version. That doesn't mean the current latest source-code version has any quality problems - it's definitely production quality as far as I'm concerned.
Development is a bit slow at the moment, but if you want to contribute some coding effort, you'd be welcome.
> what is the difference between this and the toolkit for asp.net Mvc?
Can you clarify please? What toolkit? There's nothing official from Microsoft that's similar to this.
> a lot of the validation concerns that people are having with Entity Framework, MVC and in general really are being addressed in .NET 4.0
If that's so, that's great, but I'm not sure what specific technologies you're referring to. Could you clarify? I haven't stopped working on xVal but am working slower because my other work demands (delivering an ASP.NET MVC application for a client) have