I'm sure they'll print this on my tomb stone: Maximums per page: 1 Link unit 3 AdSense for content units 2 AdSense for search boxes 2 referral buttons for EACH referral product (so that's up to 8 in total) I'd avoid using all the referral buttons because it'll look a tad desperate.
I was talking about ad units - a skyscraper is an ad unit, so yes you can put 3 skyscrapers on the same page.