the LED cans you're talking about, are they the ones that have the LED's built into them? If so you're going to have to really do the math to see if they'd save you any money in the long run.
The ones I have priced are well over $100 just for the can (Juno's and Halo's), tack on trims and labor on top of that and it adds up quick.

They would defiantly use less energy but the cost of the replacement is probably going to offset any savings you'd see.

You can get air tight IC rated cans for about $10 each. If the ceiling that the cans are in is the attic floor, and there is no or minimal insulation above the cans and/or the cans are not boxed in, then it makes sense to change out the old cans for new tighter cans and then to insulate your attic.

As for LED or the specialty fluorescent cans...I'm with hexus on that. I don't think they pay off economically at this time due to the initial high investment.

Flourescent bulbs have improved so much over the past 5-7 years, both in color rendition, start-up time, and equivalent lumen output, I definitely advise at least using flourescents with edison bases in can lights.

We'll see LEDs improve over the next few years as we've seen fluorescent improve over the past few years.

I thought I heard something on the news a few months ago about flourescent light bulbs having mercury in them, so if they break, you have a hazmat type problem. Is this true or urban fiction?

"I thought I heard something on the news a few months ago about flourescent light bulbs having mercury in them, so if they break, you have a hazmat type problem. Is this true or urban fiction?'

Yes they contain mercury

Here is a link that might be useful: Information on Compact Fluorescent Light Bulbs

Yes, fluorescent lamps contain mercury. It's a very tiny amount. Many today contain so little mercury that they can legally be disposed of in the trash. Check the label on the lamp package.

It's still probably better to take them to a household hazardous waste disposal site if you can do so without too much hassle.

Contrary to what the advertising would have you believe, real world LED area lights are LESS efficient (in terms of light output per watt) than all but old (and perhaps very cheap new) fluorescents. Compare the actual lumen output per watt. And of course they cost a lot more up front.

The good news is that laboratory LEDs are getting quite good in efficacy (l/W), and someday these will make it into stuff you can buy at your local big box store. But not today. Maybe in 5 years or so.

LED lights last longer than fluorescents, however, so they can save money where you're paying someone $30-50 an hour to change your lamps. That's why some businesses are installing them.

Don Klipstein has been debunking the myths and ad-speak surrounding lights, including LEDs (which he loves) for many years. Check out his website (below).

Here is a link that might be useful: Don Klipstein's Lighting Page

we have them in our kitchen and throughout the house. They work well when replacing regular light bulb. For some reason the flood type cfls take a minute or so to get to full brightness. Still we got used to them. Also note that these bulbs are great for placed where the rating is say 60w max....like in our closet ceiling. You can put a 100watt equivalent cfl in place of a regular bulb and get more light.