I gradually changed over all of the incandescent lights in my parents' house when I was still living with them, starting some 8 (maybe even 10) years ago. Although there were some problems with the first generation type that simply used a PL-7 CFL lamp in a cheap Type A ballast/holder, none of the newer "spiral" type have been replaced. They were even transfered to their new house 4 years ago. While the older spiral types are slightly larger than a standard sized bulb, the newest ones are much smaller. There are also dimmable CFLs, although they are still rather expensive. The only place they still use incandescents are the lights at the end of the driveway, which are the clear type in some old lantern-style fixtures where the bulbs are clearly visible.
The only problem I've seen with LED christmas lights, is that they need a decent reflector, otherwise you end up with a string of narrow colored spots.
Did I mention that I haven't changed a light bulb in 8+ years? I would have forgotten how to change one, if I didn't do it during my routine work. If you buy the decent kind of CFLs, they are waranteed to last a certain number of years, so it's no extra cost to you if they do go out.
