The POP3 access is awesome for BlackBerry users since they have a special hookup with BlackBerry. Mails received on Gmail arrive instantly on your BlackBerry with full push. This makes it great for conversational e-mail threads. You also get access to GoogleTalk, which you can also install on your berry for instant messaging those that are not on BB yet.
Another great feature (still in beta, what isn’t from Google) is their Google Apps for Domains. I recently switched all my domains to use this new service to take advantage of the spam filters offered by Google. It’s a great service, and makes e-mail hosting on your domain a snap. Unfortunately, the push delivery that the gmail.com domain offers doesn’t trickle down to your Google Apps domains yet. Bummer.
So check it out and switch to a Gmail account today!