updated 10:40 pm EDT, Tue April 6, 2010
iPad's iWork apps imply printing soon
A small clue hints that Apple may add printing support in iPhone 4.0 or another update. Support notes for the iPad's iWork apps all note that "printing directly from iPad is not currently available" and imply that it will be an option at a later date. Rumors so far haven't confirmed whether or not it would appear in Thursday's special event, though it presents the first clear opportunity.
Pure touchscreen tablets have been rare, but most non-Windows tablets have traditionally had printing as a key weakness. Neither Android nor iPhone OS have built-in faculties for printing, and many also lack USB ports. Any Apple solution would most likely involve connecting either directly to a printer over Bluetooth or over a local network using Wi-Fi.