Google Mail was originally (three years ago) just a “by invitation” service, which let Google scale it appropriately and also lent it a certain cachet of rarity. That’s been expanded over time (first 5 invites per current user, then 100 invites, then anyone with a cell phone), and now the service is open to everyone.
E-mail is a personal choice, and no solution is the best solution for everyone, but I’ve been pretty happy with going with Gmail since last year, having converted from a Thunderbird client on my PC. I recommend folks take a look at it.
(via Les)