I love the Gmail user experience (in FireFox) but as a complete email solution it's sorely lacking in one area: mobile access. A little background...
I need one view of my mailbox both online, offline and on my smartphone. That means I can't have multiple copies of my email laying around on different devices or in different environments. More importantly, it means that I need to have the ability to completely manage my inbox, no matter what the access method. This way, I don't have to perform any additional management of my inbox when I return to my computer.
I also need offline access to my email. I need to be able to read and respond to email when I'm flying and there's no way to do that without a net connection. (Although this may change in the future.)
Yes, I could use POP3 to retrieve my email before I get on a plane, but Gmail pushes down every message in a "conversation", not just new received mail. That's just a pain in the a**.
On my smartphone (currently a Treo 700p or Motorola Q), Gmail Mobile isn't an option as it requires a live net connection to the server in order to function, just like Gmail proper.
After using Gmail for about two months, I decided it was time to give it up and go back to IMAP access, but the one thing I didn't want to give up was Gmail's excellent spam filtering.
But I don't have to.
I forward all my email from my hosting provider to Gmail. Gmail removes the bazillion spam messages I get every day, then forwards my purified mail stream to my IMAP account. While it doesn't catch everything, it works a lot better than my SpamAssassin installation ever did.
How To Use Gmail as a Spam Filter:
Step 1: Forward email to Gmail
Step 2: Forward email from Gmail to an IMAP account
Step 3: Retrieve email as usual, via IMAP. Use a desktop client, webmail client, smartphone or SSH shell.
Step 4 (Optional): Periodically check the Spam folder in your Gmail account to ensure that it didn't capture any false positives. I check mine a couple of times a day.
UPDATE: I forgot to mention another important benefit of doing this: with almost 3 GB of storage in Gmail (and growing), you automatically have a searchable index of all your mail.
[tags]Gmail, Spam, Smartphones, FireFox, Broadband, Web Applications, AJAX, SpamAssassin, Spam Filtering, Tips, HowTo, Email, Productivity[/tags]