Dropbox is a free service (for up to 2 gigabytes) that puts a magic folder on your desktop—of every machine you own. Including your tablet or phone.

Anything you put in there magically shows up in all the others. There’s no reason you couldn’t transfer your stuff from PC to Mac, 2 gigabytes at a time, by dragging it into your Dropbox folder on the PC, and then opening the Dropbox folder on the Mac a few minutes later and moving your files from there into their new homes.