Honestly, I buy most stuff over the net. It's not so much the cost ... it is the convenience and variety. I commute by bike most days and there aren't a lot of suitable LBSs near my house. It's a lot more convenient for me to do it myself than make a special trip.

That works for me, because I do 99% of bike maintenance myself. If you're someone who doesn't do all your own maintenance (most folks I know), I'd strongly recommend a good LBS instead.

Bike purchases are a different matter. Fit is important, so IMHO, they should always be purchased at a brick and mortar store.