Gmail, by far the most innovative web-based email, has taken the marquee one step higher. Now offering IMAP as a feature. For those not familiar, an email server is typically setup as POP3 or IMAP. The typical email account from your local ISP (ie. Time Warner, Cox Communication, Earthlink, etc.) is usually POP3. That is, when new emails arrive, they are stored on the POP3 mail server until you read(retrieve) it, the moment you hit the send and receive button to retrieve it, the email the emails will be cleared from the POP3 server. So if you download the email from your personal computer, that email is going to stay with that computer; you will not be able to download it again or view it from the "webmail" option.
IMAP is usually a more professional option. This is something your work email is likely to be set up as. The IMAP server is the host of the email, you can view(retreive) it via a webmail interface or from a computer or any other device that is configured to read the email. Unlike POP3 servers, retreiving an email from a personal device doesn't wipe the mail off of the server, giving you a wider mobility.
So back to the main story, Gmail is now available with this option. Some users claim that they are not seeing that option yet, while others are suggesting you to log on and off Gmail a couple of times to see that option. I am seeing this option fine within my "Settings"... see screen cap.