>Amazon can be scary good. A few years back I crashed my road bike and needed an obscure part. Tried lots of local bike shops - no dice. Amazon to the rescue: http://www.amazon.com/Shimano-ST-5500CA-Left-Cover-Plate/dp/B001GSQMC0
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>I think a lot of bricks&mortar dry-goods retailers have good reason to be very afraid.

Yes and no. The modus operandi of local parts shops (for cars, electronics and whatnot) is that they all operate at minimal shelf level - and get whatever you may want from a catalog, delivered tomorrow. Country is small enough that this promise holds true. Their advantage is the knowledge - they know which part you may need, which brand has what faults, which is chinese junk and which is the german brand chinese junk. They have the databases of pretty much everything you may need - you only need to know the model and the year. Now it's only a matter of their suppliers having the stuff, and they usually do. It's the long tail sale logic applied to brick and mortar stores (real brick and real mortar, not just a bunch of 2x4s with drywall slapped and dressed in half brick veneer on the outside).

This sits fine with specialized shops where you expect the clerk to know more about the stuff than you do - and you do there to specifically take advantage of that knowledge. Not sure how it would apply to, say, places that sell books (can't expect the clerks to have read all the books), shoes (they don't have the same foot shape as you do) and general groceries. In those cases, you got only what's in the store, and over the years I saw the choices dwindling.

As for the online price vs store price, I've seen different behaviors. I've seen a car price going down to the online price within 5 seconds, and a battery for a gadget going from $60 in Radio Shack to $20 online... seems there's no set custom yet.