Of energy efficiency and dimmers
Apparently we should use CFL because "conventional" bulbs are an inefficient form of space heating, as well as lighting.
I have it on good authority that using electricity for generating heat is 2.7x more carbon intensive than gas space heating, and more importantly it's 3.5x more expensive.
Of course you should steer clear of the cheap CFLs like the plague that they are. Unfortunately those cheap ones were exactly what British Gas sent out to all their customers, so they're what most people first have experience of.
A good CFL has a nice colour rendition, and doesn't flicker at all. Check the CRI of any bulb you're considering, check the colour temperature, and if you can test it for yourself to see whether it starts cleanly and quickly.
Interestingly there's a fair amount of variation in performance between individual bulbs of the same model in my experience. For example that British Gas CFL package contained several apparently identical 60W (equiv) bulbs, one of them starts instantly and builds up to full brightness in under a minute; the other flickers badly during startup and takes several minutes to get brighter, yet the make/model is identical.
Personally I don't see the slow start characteristic as an issue; I don't usually want full brightness instantly myself, it's uncomfortable.
As for flickering once the bulb is on; with a good bulb it's negligible IMO. I can see flicker on a CRT up to 80Hz or so, and none of the CFLs here seem to flicker to me.
As for dimmables; you need special bulbs for that. No idea how well they work, as I don't use dimmers.