I dislike attendee. In arts marketing (in the UK, anyway) we tend to talk about attenders to differentiate them from intenders (people who are sympathathetic to an event but may never get round to attending).

I think it is just the rise and rise of business speak that makes these things grate so much. Conferences have delegates, performances have audiences, schools have pupils - I'm not sure if we need a word like attendee.

Incidentally - I spotted Jackie's suggestion in Information to install Gurunet and a couple of simple right clips came up with this:
"USAGE NOTE: Reflecting its origins in the French passive participle ending -é (feminine -ée), the suffix -ee was first used in English to refer to indirect objects and then direct objects of transitive verbs, particularly in legal contexts (as in donee, lessee, or trustee) and military and political jargon (draftee, trainee, or nominee). Beginning around the mid-19th century, primarily in American English, it was often extended to denote the agent or subject of an intransitive verb; for example, standee, returnee, or attendee. Although the pattern is very common and a number of these coinages, such as honoree, deportee, and escapee, have become widely accepted, in general they retain an informal character as jocular nonce words."