Gmail

Maaaan GMail is tops. I got invited last week as well and I'm really psyched. Among *many* other features, it groups multiple replies into one handy threaded conversation!! How awesome is that?!?
 
Google pretended it's in beta form in order to stir up excitement as people scrambled for Gmail invites. When the first wave went out several months ago, they were being talked about on every message board, traded back and forth, and even sold on eBay.

MARKETING!
 
Alex is right, it was a genius stroke of marketing, it created a great buzz leading up to the IPO.

one thing I appreciated was when Google came out with the enormous storage size, some of the other free services rushed to imitate. wooooo

threaded msgs
large storage

right now the Google people are the cutting edge of search engine and email provider.