So far you had two option to access your Gmail account. The obvious webmail through a browser and if you wanted to use the Mail.app's features and speed you could download your Gmail through POP. Now, you have a third option — IMAP.

It's not yet available to all users. You can try to log-out and log back in to see if you have the IMAP option available already under Settings / Forwarding and POP/IMAP. To set up Mail.app for IMAP Google provided a detailed tutorial. It's pretty straightforward.

Now, what's the benefit of IMAP on Mail.app over POP on Mail.app?

• You can access your mail from any number of machines with IMAP. This is great if you have a laptop for travelling besides your desktop Mac. POP is usually set-up for one computer only.
• The read status of your mails is followed upon whether you're checking your mail in a browser or in Mail.app. With POP Google will not be able to tell if the message you downloaded has been read or not.
• Messages appear faster in your inbox, because only the headers appear. This is great if you are on a slow connection. For example using your mobile phone to get internet on your laptop. With POP you have to wait till the whole message gets downloaded.
• It handles very large messages better.

What's the benefit of IMAP on Mail.app over using webmail in a browser?

• You can browse your email and create replies even when you don't have internet connection. Huge benefit when you're on the road.
• You can use html signatures and email in Mail.app. In webmail html signatures are only possible with Firefox and the Better Gmail add on extension.
• Depending on the speed of your connection Mail.app is usually faster to browse than clicking around in webmail.
• Mail.app has powerful drag and drop, webmail doesn't.
• You can use Mail.app's integration with other OS X applications and you can use Mail.app's features that are not available on webmail.

To me the choice is clear. Let me know your preference!