The previous post about the servers coming back online seems to have been slightly premature. Many, if not most servers are still offline, and the current target for bringing them back is 6 PM PST/9 PM EST. Be aware that this target has been pushed back three times since being originally set for 2 PM PST/5 PM EST today, so I wouldn't count on being able to play any time tonight necessarily. And when the realms do come up, I wouldn't expect them to be super-stable; the few realms that are up right now are having all manner of crashes and other difficulties.
That said, I'm can't really be mad at Blizzard for any of this. This is possibly the largest patch in MMO history, as one astute commenter pointed out; it would have been extremely optimistic to expect it to go off without a hitch. We'll be back sooner or later (unless they decide to just leave the servers off until Wrath hits), and we'll have plenty of new toys to play with. In the mean time, why not check out our voluminous coverage of the patch, or our handy all-in-one FAQ?