I was just watching a great introduction to the iPad with Alex Lindsay and Andy Ihnatko where Andy revealed that the iPad can't print.
At some point, some applications might individually support printing, but the iPad comes with no printer drivers and has no capability whatsoever for printing.
Ihnatko described it as a way to make sure the iPad stayed stable, but that's one feature that destroys the premise of the iPad as a replacement computer for people who just want a simple computer to read email, use Facebook, Twitter, and browse. At some point, everyone needs to print.
It also severely limits the iPad's use in government and enterprise. To bring documents into the iPad, the primary mechanism is iTunes, which is, itself, quite limiting. I think most of us just assumed easy printing would be a no brainer -- what with Bluetooth and WiFi on the device.
There's no doubt the iPad is a beautiful toy. But without printing, that's exactly what it remains. A toy.
Update: We may have a winner. I've gotten a number of reports of an app called PrintCentral that provides printing services for the iPad (and iPhone). It's $9.99 and may solve this problem. If it does, it's well worth the price. Honestly, I'm relieved, because despite the naysaying (my own included), I really do want this form-factor to succeed.
Disclosure: the author derives a small personal income from Apple iPhone applications.