One page. It's a one-page business card. The longer your resume is, the less likely someone is going read it. It's not an exhaustive blow-by-blow account of everything you've done - just the highlights from college onwards.
Most people spend around 30 seconds to 2 minutes going over a resume. That's it. Just because it's longer and verbose doesn't mean they will spend more time to read it - they will simply skim it or even worse, completely ignore it.
Also the resume has to be accessible. Jargon doesn't really help you. If you Stephen Hawking can explain String Theory in layman's terms, anyone can explain their job without resorting to jargon.
Put it this way. If you feel that you need 4 pages to explain your history, why stop at 4? Why not just expand it to 8, or 10 pages or more?
Again, think of your resume like a one-page business card.
Alex Chu
alex@mbaapply.com
www.mbaapply.com
http://mbaapply.blogspot.com