This is a really cool program. I keep Mail.app open all day, and I'm not a fan of multiple desktops through spaces on my iMac with a second monitor setup. It's a good way to keep things visible without losing a lot of screen real estate.

No, it really doesn't. This is designed as a mini interface (ala iTunes' mini player view) for mail. Mail.appetizer is more like a growl notification. The default keyboard shortcuts also work in MiniMail since it's just a mini version of the actual app.

Mail.appetizer. Free. Effectively does the same thing.