Google use Gmail in their offices rather than Outlook. I can see why. Gmail is simply very good. I'd be lost without Gmail.
Check out my spam count. Over a quarter of a million messages. Gmail deletes spam after 30 days too. This is a record for me and I blame Christmas. Christmas is the season for spam.
It isn't just my Gmail account which collects mail. My main domain forwards all emails to Gmail. I then pop the lot. I still have the run a baysan filter on Thunderbird but without Gmail I'd be waiting hours for my email.
The Gmail contacts online feature is really handy. I like to see the little green ball light up to show that a contact is online. I would not be surprised to see if Google roll out that feature to other areas; imagine Google Groups or even Blogger alerting you when friends are online. You could leave a little green Google light behind with each comment you leave on a blog. The blog owner would be able to see if you're online (if you wanted) or not when she reviews the post. AOL have done the very same thing with a light up flower icon for AIM and Yahoo has their smilie faces.