I don't think qualifying has anything to do with your SL account -- the only thing you're asked to provide is an email address. And I didn't use the same email address that I'm registered with in SL.
Anyway, I tried it a couple of times last night, and twice today and got on with no problem. I think its a really interesting concept -- letting folks jump right in to explore, without having to go through creating an account and install the viewer first. Also, it *seems* that things rez a lot faster in the web viewer. Pretty cool stuff. (I tried it with Chrome on Win7 - 64 and Chrome on XP -32.)
I think some people are under the impression, that this will be an alternative viewer and should have many of the functions as the regular viewer. But the original post seems to make it clear, that this is intended to get new folks in to try out SL, as easily as possible.
@ZenWarrior Fuosing: I noticed that also, regarding the choice of avatars, and I agree