In reply to JLS:
In my experience there is always something to be learnt from a guide, but you have to be prepared with a range of routes you wish to do, discuss your goals beforehand and start the day(s) with an open mind and a long list of questions, ready to ask always why we are doing, what we are doing. Obviously the snow, the weather, the gear, the altitude - you just have to learn over time and experience but asking a guide to teach you as you go along is really useful! All the guides that I have been in contact with are great professionals, you can't go wrong really!
Experience is something you can't buy but you can learn from.
If you are just 'taken up' or attend a course with a bunch of beginners to be introduced to the Alpine climbing, then it is a bit wasted money. A guide is more than happy to switch their brain off and only talk through their regular chit-chat while going through the motions. Even so, if one day out like that gives you confidence to go climbing with your friends afterwards, then it is worth it!