In reply to grumpybearpantsclimbinggoat: I just purchased some Brooks GTS 13's yesterday, from Runners Need.
I paid a bit more for them in store, but I spent 40mins on and off the treadmill plenty of times, and received some very good advice. They have corrected my MASSIVE over-pronation immediately, both on and off the treadmill analysis. Those who say that the OP shoes are a waste of time obviously haven't struggled through injuries and pain due to over-pronating! The science makes perfect sense, as does watching the video analysis if your seriously over-pronate!
Obviously it's up to you. If you are having problems due to your over-pronation then I'd go for a supporting shoe and start enjoying your running again!
If your running shop has taken the time to do the analysis and recommend a shoe, and analysed you again in the new shoe, I think it's worth paying extra for that service. That treadmill and video isn't free. Plus, not every OP shoe is equal. Some might correct more than others, some might correct in the wrong place (ie cause pain). Again, well worth trying them on teh treadmill in store and getting another analysis done to compare them.
Next time I'll get them online if they are much cheaper, but I've already paid the "premium" during yesterdays fitting.