Saw this on BBC... thought someone might be interested in giving it a try.
(you may be able to get on a list for other sizes if it comes up, someone else said they did Pullups recently)

HTH

I just got in on a great diaper study for Owen & they're looking for more participants. You get 3 bags of diapers over the course of 3 weeks and fill out a short questionairre at the end of each week and set up a "phone interview" time to relay your questionairre answers to someone at the diaper company (takes about 5 minutes each time).
You get all the diapers for free, you keep any extras you haven't used during the course of the study, and they send you $10 at the end of it, too. Not a bad deal!
If you're interested, call Sheila at 888-342-7372, x634.