In this recent post the opinion was expressed that 'spectate' is an unnecessary back-formation from spectator, because we already have verbs such as 'watch'. I respectfully disagree, in some circumstances at least. To spectate is to watch an event, as opposed to competing in it, especially if one could be doing either at the event in question, depending on circumstances at the time.
Maybe it's a UK thing, but if I was at a motor-racing event watching, then I would have to specify what and where: ie was I by the track watching the current race, or in the paddock watching the teams work on the cars? To say I'm spectating covers the former only (and furthermore carries the implication that I'm only watching as opposed to producing any form of written or visual report on the event).
Specialist language perhaps, but I find it a useful word.