I guess I wouldn't call myself die-hard, but I'm an established Chrome user. Speed helps, but it wasn't the main factor for my preference.
Having access to new standards like WebGL is very nice (I don't care if FF and Safari have it as well; it's an example for anything in the future). And they get me with simplicity, as others have said. Speed, Security, Simplicity, Stability. The entire attitude of it all really gives off a good vibe.
All the cool little additions help. Desktop notifications, location tracking, speech recognition. Sync, oh gosh, sync. That was a big factor, indeed it was. I guess I could use FF for this purpose, but alas, you can't run FF in Chrome OS, now can you (not that I would want it any other way [and no, I don't want to install Ubuntu on my Cr-48 just for that purpose])?
Omnibox, Chrome Instant, drag-and-drop, compact navigation (currently in the Canary build), access to experimental features (through about:flags). I could go on forever about the endless exclusives (IE9 has the Onebox, sure, but it's too small for my tastes. And granted, Firefox has about:config, but about:flags is easier to understand).
/ramble