I've bought several LED bulbs to try them out. The number one problem is they are about half as bright as necessary, so you need twice as many bulbs. But if you've got existing fixtures, there aren't twice as many sockets for the bulbs.

The second problem is you cannot install them in enclosed fixtures - because they'll overheat and fail. They can only be installed in open air fixtures.

These two issues pretty severely limit where they can be used.