And you know, personally, what I found to be the killer UI feature? Not labels (great that I can create my own a la Netscape/Mozilla) or "conversations", but Keyboard shortcuts! Awesome! I can type 'c' and open a compose window. I can jump to my new mail. Best of all, I can hit '/' and jump to the Search box. What are a few targeted ads in front of all this :-) ?
Right now, I'm only using 0% of my 1000 MB space.
Update: Day 2 and I've already received my first spam mail - is it part of the "Beta" testing or are spammers that quick on the uptake? Also shot off a couple of "suggestions"...