Everyone is a-buzz this morning with the news that GMail may be adding support for IMAP. There are two main ways you get email off of (or out of?) the Internet and into your email program: POP and IMAP. POP is by far the most common for average folks like you and me. But IMAP has some powerful features that may be important for you.
Among other things, IMAP support lets you synchronize your email between computers, handhelds and the web. Mark a message read on one computer, and it will show up as read on another. Move a email folder from one place to another and it will replicate on another.
It appears as though GMail is adding this functionality. Here's a screen shot from DownloadSquad: