[citation][nom]WheelsOfConfusion[/nom]Okay, about the mercury: CFLs contain so little of it that, environmentally speaking, they more than make up for it with the amount of coal-fired electricity they save. Coal-burning plants put out more mercury than CFLs do, just by producing power. And CFLs only release mercury if they're broken. Furthermore, they don't release ALL the mercury if that happens, because as it gets used the bulb's tube actually binds up most of the mercury vapor in a form that isn't release when a break occurs.[/citation]Great points. Here's some additional info. According to GE's website, a "typical" CFL contains about 5mg of Hg. A modern home thermostat contains about 500mg of Hg. Even if broken or improperly disposed of, it takes 100 CFL bulbs to potentially release as much Hg as one improperly disposed of thermostat.
Each 15W CFL lasts 6000 hours and saves 45W (vs the 60W incandescent it replaces), which is a savings of 270KWh per bulb. I'm not sure how much coal it takes to generate that much electricity (plus 5-10% for distribution losses), but I'm pretty sure that burning the coal will release more than 5mg of Hg. Granted, hydro, nuclear, wind, and other sources don't have the same return, but in much of the US, coal is the major source of electricity generation.
I live in Texas, so I get a secondary benefit from using CFLs, they generate less heat, which means I use less electricity cooling the house. I don't get that benefit when I have to heat the house, but around here, we use air conditioning far more than heating. Bottom line is that CFLs save me a lot of money.
LED looks promising, but it's not quite competitive in terms of light quality, color temperature, and purchase price with CFL as a replacement for incandescent bulbs. In the next 5-10 years, LED might even replace CFL, we'll see. ESL is interesting, but I'll wait and see. In the mean time, I'm a CFL user.