Back in the 2.8 days, when you got on the beta, the only way to stay on it was either the Beta Testers Plugin or manual updates.
Apparently now, in 3.0, I get this:
An updated version of WordPress is available.
You are using a development version of WordPress. You can update to the latest nightly build automatically or download the nightly build and install it manually:
So I guess it SHOULD work, though I recall it has always been a bit tetchy about checking what the latest and greatest was. I think it's a false positive, or perhaps since the subversion repository is constantly getting updated, it's just going to be weird like this. I don't know if it's checking against the SVN or the build, though.
Its rather pointless if this url is going to serve 2.9.2 IMO - what's the point of having a development version at all? I don't think they would do that, though I haven't actually checked the code of what I download...
Not really. Most people never test the dev version so they don't care. :)