I love Gmail: it's quick, efficient, reliable and simple.
For all its perceived limitations Gmail is -- for me at least -- so much better than anything else.
The Archive function is what does it for me. For my money, this works much better than filing things in folders (and you can always add labels).
For work, I still have to put up with Outlook Web Access, which is incredibly slow and (in our installation, at least), has no search, a horrible move-to-folder interface, and is liable to log you out with no warning.