In reply to joeramsay:
I think they are not quite as strict after the 15 sept, but if you het kicked out, head over to the pines campground, look for a site with only a few people in, and ask if you can share their site. Try find people who are staying there a while so you dont have to move around too often. You could maybe offer them some cash, but they will usually just let you stay for free.
You can go to the campground reservations and buy a site in the pines that the reservation has been cancelled. Cant remember how much, but if you are a group works out similar price to camp 4. Max 6 people per site.
If you are just bivying, i would just bivy in an emptyish looking site in camp 4, and make sure you're up and packed up by 8. You'll have to make friends to use bear lockers for your food, or use the ones near el cap or otherwise. I did this for 2 months without any trouble.
Some people also bivy in the boulders,but if ypu do this make sure you go a really long way from camp 4. The rangers know all the good close spots so be careful.
Rangers also sometimes patrol the base of el cap. If your found there they will tell you to start climbing immediately or get a fine.
Worst case is you'll get fined, but thats it. Never give a false name or you will go to the jail and then court, then never be allowed in the US again!