[Snowleopards]

I know a lot of users want to try AirPrint. On Mac it is easy to enable it.
For Mac best thing is Printopia (Not free (Supports ALL PRINTERS)): Printopia - Share Your Mac's Printers to iPhone and iPad - Print from iPhone - Ecamm Network
Second is (Free (Not Support all printers)): Download AirPrint Hacktivator for Mac - Activate AirPrint by adding or removing the required files. MacUpdate Mac Software Downloads

What can do Windows users? There is solution: How to Install AirPrint to Enable Wireless Printing on Windows? | Jaxov
Don't forget enable Printer Sharing, then restart computer.