JamieBrown - 9:16 am on Apr 14, 2010 (gmt 0)
It is 100% about the risk to your revenue. Paid links do definitely work - especially when used in conjunction with other more "natural" link building techniques to spread out the link pattern a bit. And the increase in SERPs can really bring you a lot of cash on the right terms.
But I've personally seen a number of sites wiped out in one fell swoop because they were link buying too aggressively and something flipped somewhere.
If you have lots of sites and you don't mind possibly losing one in the medium term for some short term gain, then go for it. If that site is your livelyhood, I wouldn't risk it at all.
Try buying expired domains with authority links instead! That's my favourite kind of kind buying.