Gmail is very impressive, save for one rather serious flaw.
Their spam filtering is really, truly, awful. This is quite surprising -- most of us thought Google would do a great job of spam filtering. Astoundingly, they're far worse than Yahoo, Spamcop, or my personal ISP (visi.com). Recently my inbox has had 25 spams a day -- compared to 3-4 spams in the same mail stream (my messages bifurcate) managed by visi.com. Nor is VISI producting too many false positives; they do pretty well.
Until GMail gets its spam filtering under control I can't recommend them to anyone.