Frequently when I tried to order something that is supposedly in stock, I get confirmation, then, a few days later a cancellation because the object wasn't in stock. I realize this isn't directly Amazon's fault since they are not the store, but it is problematic when you are trying to find and buy a specific item - I mean not so much as an email asking how to proceed, just a flat out cancel!
Over hundreds of transactions, that has never happened to me. Not once.
Lastly, if you are looking for information about something, particularly technical or specific details, you might as well go somewhere else - you won't find it here. It is a search to find something that *might* fit, then another search (via google) to find details, then a search back at Amazon just to buy it from someone else. For all that annoyance, I will just go to the manufacturer, find exactly what I want, then Bing or Fruggle it to find the best price. If Amazon happens to be it, good for them, but I am no longer looking there.
You can often get lots of useful information from the extensive reviews on Amazon.
I usually research what I want first, then look for it on Amazon to take advantage of (usually) low prices, (often) free shipping, and (always) reliable service.