I buy from my LBS where it makes sense. Personally I don't mind paying a little more to support the local guy, especially when he's helpful like my LBS is.

Trouble is there are deals so much better online. When I had my chain and cassette replaced the LBS charged me £34.99 for the cassette and £19.99 for the chain. Online they were as cheap as £16.99 and £14.99. The only reason I went to the LBS for that is because I had a long ride approaching and didn't want my first attempt at changing the cassette to be shortly before such a long trip.

I just bought some brake pads online. Online price £5.99, LBS price £14.99. I can't justify paying that kind of markup to the LBS.