I have never heard "Facebook" used as a verb ("to facebook").
Photoshop means "edit a photograph", and Google means "search the web".
Facebook provides too many diverse functions to be easily verbed. Would the verb be transitive or intransitive (e.g. "I facebooked all day" vs "I'll facebook you")? In the former case, does it mean "update my profile", "look at friends pictures" or "search for new friends"...? In the latter case, does it mean "add as friend", "send a message", "write on the wall", "ping"...? It is unclear. There is no single defining activity that Facebook is used for or a clear result it produces.
Similarly, spreadsheet or database program names ("1-2-3", "Excel", "Oracle", "MySql") are rarely used as verbs. These programs, like Facebook can be used for diverse tasks.