I wouldn't buy a bike online because of fit and service ... and I try not to buy parts online because that's where the LBS makes their profit. (I have my limits ... as when I got my saddle for something like half of MSRP... bad me ) As I understand it, complete bike sales are a LBS's "loss leader" to bring customers in for the parts, service and accessories.

Clothing is another thing. I really prefer to buy local, but I don't live anywhere near a shop that has a decent selection of women's gear, and returning something bought online (TE! TE! TE!) is SO much easier - often if I special order something through a LBS it's entirely nonreturnable.