Okay...I've been using it now for over a week, and here are some first impressions:

The Good:

• It's cool.
  
• It's fast.
  
• It's intuitive.
  
• The searchable feature is cool, though it's too early to really tell how it's going to function. I've only got a handful of mails archived.
  
• When you take actions, they are executed immediately...no checking a checkbox then hitting a button, then confirming to delete something or archive it
  
• The advertising is so unobtrusive I didn't even notice it for the first five days. This may turn out to be a negative. If they don't get a lot of throughput, they may make them louder and more garish...let's hope not.
  

The Bad:

• I've got to log in every time I visit GMail. They need a cookie to remember me...I'm assuming they'll add one.
  
• Spam. I've already received 13 spam e-mails, more than legitimate mails. The filter has caught 10 of those, with no false positives, but 3 made it into my inbox. Incidentally, I reported the first of these as spam, and the next two were remarkably similar, from the subject line to the body. So apparently their filter, even with reporting, still needs some work. Hopefully it will improve.
  
• Attachments. Stuff attaches fast and delivers smoothly, but I often mail docs and files to myself and was looking forward to using all that storage space as a form of backup. Small files work okay, but stuff bigger than a couple meg doesn't, which is a bummer. This may have more to do with browser/ISP issues than with GMail...dunno.
  

Anyway...that's it for now. I don't know if Google will actually be soliciting comments from beta users, but there you go, guys...you got some anyway.