Not too bad so far when I tried it.  You can fit in driver's license/credit card and some cash.  You can also put in a key or 2 if you want, but it makes it really bulky.  I was also able to fit it over my ankle...it just looks very weird :P  Zipper was a little annoying and it's not as streamlined as I hoped, but I think it will do it's job admirably.