I'd venture to say that just about anyone who knows me received one of these at Christmas! They're just that cute and easy to make! I started out with the SU! Thoroughly Modern file folders, but three orders later I decided to stop waiting on Mr. Brown and headed out to Office Max and Staples to see what they had. Oh my, I was in file folder puppy love, lol :)
This set of folders came from the clearance shelf at WalMart. The quality isn't as thick as the other sets, but I didn't find that to be a big deal since they're a disposable item. I also didn't realize until I got them home and opened that the insides had large polka dots - how cute!
Two tips I found helpful... I cut the left and right sides of the bottom flat that folds up at a slight, maybe 1/4", angle before putting adhesive on it. I also found out after my sister actually used the flap to hold things that by using a foam tape (her idea!) instead of flat adhesive, it makes it easier to 'use' the pocket on the left...gives it a little wiggle room!
If you're using a Scor-Pal instead of a paper trimmer with a scoring blade, you can find revised instructions On Papercraft Planet that might help. Then again, I tend to do things backwards, so maybe it only helped me ;)