Quite a good article here...
http://news.bbc.co.uk/1/hi/magazine/8406923.stmIt adds something I'd not thought of before, and that's the non-unity power factor. Put simply, that means the power dissipated as heat by the CFL bulb is less than the product of the voltage across it and the current through it, because the current and (AC) voltage are not perfectly in phase with one another. You're not charged any extra for that, you're only charged for the energy dissipated in your home.
That sounds good, doesn't it, you've drawn more current than you're charged for? But it's not - the current is real and flows through the supply network, resulting in heat-loss in the electricity supply system. Looked at another way, low energy CFL bulbs contribute directly to heating up the great outdoors and the atmosphere, whereas traditional light bulbs have unity PF and contribute cheifly to indoor heating, where heating is usually a good thing in any case.
There does seem to be light at the end of the tunnel (no pun intended). I noticed some LED bulbs in B&Q - currently only 'equivalent' to 10W incandescent, but hopefully they'll improve. The halogen bulbs also shouldn't suffer from the PF issue.
- 7LM
edit: PS I just noticed that link was already posted by HP. Still worth emphasising the PF factor aspect, though.