I take the Tonalin brand of CLA (conjugated linoleic acid.) They have some nice summaries of the research on this link, (yes, they sell it, but they certainly aren't the only ones, and the free book is very well documented.)

http://www.wellnesspartners.com/tonalin/?s=g&p=cla

Personally, I have taken CLA for two years this coming May. For I year I took it and made no other changes in my lifestyle, and lost maybe 15 pounds in a year. Then I continued taking it while on Atkins, and lost 10 pounds a month until I was near my goal weight, at present.
I think it's great stuff. I know people who started taking it and their allergies got bettter and their workouts seemed to be more effective. I also know people who claim it didn't do a thing for them, so Your Mileage May Vary.
Considering all the enhanced metabolic effects, such as decreased insulin resistance, I think anyone should see if it works for them.
I'm extremely pleased, and it is the only supplement I consider important enough to take every day.