Just finished 16 years RAuxAF service a few months ago. Would echo what's been said already....on the whole had a great time, some great experiences...you will get out what you put in (for me that varied a bit over the Years).
Was called-up once during my time (4 months in '91, in UK supporting Gulf Ops), which was actually a great experience....only bad bit about it really was the stuff that
kbf has already mentioned, and the fact that Admin is so slow in the MoD generally (if they were a business, they'd go bust in no time!).
My former Sqn is now under it's 3rd call-out (the '91 one was the first), and that's a sign of the way things are going....no point in being in the Reserve Forces if you can't answer the call (or brown envelope!) when it comes....think seriously about that before you sign up.
Otherwise, go for it and like me, you will be able to go into the Office on Monday, and when asked "what did you do at the weekend?", say "went to Bosnia actually, how about you?!!"