^ Money is pretty dirty and unhygienic, not the best idea for stuff you are going to snort.
That said, a friend of mine does this, and it does work pretty well. I use small bits of other paper instead, from a notepad or something - have noticed sometimes if the crystals are particularly "sharp" it will start shredding the paper...
Having done that, I'll generally use some cards or razors to finish the job. I did used to be a bit concerned about the razor thing too but haven't injured myself yet. Is it just me though or does ketamine often have a kind of static charge?? I find it has a tendency to stick to the cards far more than other narcotic powders...
Writing this post is making me want to get some ketamine haha... gotta hold off for at least another few months though.