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