Google has been enabling IMAP access for everyone that has been using GMail. IMAP, like POP, is a method of downloading mail from a mail service. POP works really well if you just use one computer, but it's a nightmare if you use more than one. And you know, the iPhone is a lot like a computer, enough that using POP on it has kind of been a nightmare in terms of checking my work email. The option for IMAP hasn't showed up on my account yet, but it's showed up for Dieter, and he has a good account of how it works up at WMExperts. If you prefer, there's also an official Google video available at YouTube, catered specifically for iPhone users. If you want article help on how to install everything on your desktop email, GMail has posted a help file on their site.
And now, that video for any iPhone users out there: