Here's a great response from the Bicycling Magazine Forum:

Originally posted by velobro.1:
Fitting is extremely important. How important? Well, my partner and I have invested tens of thousands of dollars in developing a fitting system in our shop that we think puts us at the zenith of bike fitting. Bike fitting is important for three primary reasons. 1) Efficiency. A proper fit will allow you to harnes that tiny bit of power we as humans produce and channel it efficiently to the bike. 2) Comfort. If you aren't comfortable, you can't be efficient. 3) Injury prevention and mitigation. Poor fitment can invite injury. Proper fitment can't overcome injury, but it can in many cases mitigate the symptoms caused by injury or fitment injury. For example someone with a bum knee, bad back or painful neck might come to us to seek a fit that might mitigate the pain and damage.

Okay...so what's a good fit? Well, to us, it's as much as a 15 hour, $500 investment a customer might make. For some crap shops, they plunk your *** on a bike, grab an allen wrench and make a couple adjustments by "eyeballing" the fit before sending you out the door. We might use cameras, lasers, computer sensors, IR cameras, watt meters, flexibility tests, even blood tests to determine "fit."

Long way of saying ---- NO. Not all bikes will fit you. Not all shops will know how to fit you either. They may think they do.