I have painted cars with professional equiptment and expensive paint and also with spray cans. Using the proper equiptment and paint makes a huge difference and is less work.
It is possible to do a very nice paint with spray cans however it's alot of work to wet sand between each layer. Also in order to do the final colour sand you have to wait a few months for the paint to cure. It is also not as cheap as you would think. It takes alot of cans and it would probably end up being cheaper to do it with cheap equiptment and cheap paint. The nice thing is with cans it's easy to grab a can that matches if you need a touch up. And it is less effort do colour match small items on the car.
This orange car I painted with off the shelf cans.
http://pg.photos.yahoo.com/ph/nigesrota ... pg&.src=ph
This blue car I painted with professional equiptment and PPG paint.
http://pg.photos.yahoo.com/ph/nigesrota ... pg&.src=ph