Imagine hotmail on PCP and steroids.
They give you a gigabyte of space, as opposed to 2 megabytes you get with a free hotmail account. You can't really just "sign up" and get Gmail, you have to have somebody give you an invite. It's from Google....it's still in the beta stages, so that's why it's not open to the public. But it seems like everyone has one now. Lol.