They're more likely to lead to headaches than big sales. Don't scrimp on planning. Foresight is a lot better than hindsight. Re-educate middle management and make sure they're with the program. Our advice is to get them out of the way.
Scale is king.
Make sure a site can handle at least two or three times the amount of traffic you expect to receive. Don't try to be everything to everyone. Pick something and be good at it. Work with adults. Don't slap e-commerce on top of legacy systems.