For me, aside from wheel trues, headset work, maybe full overhauls, or if you're VERY in with you LBS, just buy the tool. At most shops (around here at least), the tool itself is either cheaper than the cost of service, or using the tool maybe twice would pay for itself.

Even if you're unfamiliar with the work being done, fixed gears are simple enough. With enough grease, the proper tools (if not, you're going to break stuff), and occasionally double checking which threads go which way, plenty of work can be done at home.

Hell, I'd almost rather buy the tools just to use them once. I understand that some people come into a shop and say "something's wrong, fix it," but it really stings when you go into a shop knowing exactly what you need, knowing that it will take them 5 minutes at most, and still hearing "ok, that'll be 12 bucks, please."