This is the best email program ever. It gives you a ton of storage space so you never have to delete emails and there is a sensible archive strategy so the emails remain accessible without cluttering your inbox. You can also do text and video chat right from your Gmail page. If you are worried about all of your other email accounts, don't. Gmail allows you to consolidate all your accounts such that you can send and receive from any address (this will be the subject of an upcoming post). Lot's of other great Gmail features are available and will be the subject of other posts.
1. 25MB attachments
2. No email quota (never delete a message)
3. Manage all email accounts from one place
Science use case:
The chat features and sending large email attachments make collaboration a snap. Your Gmail user name and password will also be your gateway to the rest of the great google apps including Reader, Docs, iGoogle, etc... (reviews coming soon).