I'm going to have to use one of these, and I read up on it, and the jist of it is that I will have to fill out my own taxes or something.
The beauty of 10-99 is that the employer doesn't take out any taxes when they pay you and you're able to write off just about everything you do. You make web sites? You've got home office rent, all computer equipment, utilities like electric/internet, books + magazines for research, gas if you have a car, uniform (everyday clothes), etc.
The employer files the W-9 form you filled out telling the gov't how much they paid you, then they send you the 10-99 that you need to include when you file your 2006 tax return. I'd suggest heading to a place like H&R Block and they'll help make sure you have written off as much as you possibly can. The IRS is going to try to take about 1/3 of what you made by default, a crafty accountant can write off enough stuff to have you break even - or possibly get some money back. Those mini mall accountants are much cheaper than you'd think. Also, walking in to talk to them is free.