Running on manmade surfaces will only damage your joints if you're running with bad form, i.e., heel-striking. Barefoot Ken Bob has run tons of marathons barefoot on pavement, but he does it with natural form, on the balls of his feet, and his joints are doing great.
I haven't noticed any problems with blacktop pavement--just cement, which is apparently denser and therefore harder and less forgiving. Now that I'm used to walking and running in bare feet and flat-soled shoes, shoes with heels like Sully's feel awkward and clumsy and tip me foreward and out of balance. So shoes with big cushy heels are not a good solution re: cement for me. I've been giving my right foot a break by trying to walk on the grass beside sidewalks wherever possible and it seems like it's slowly recovering.
I'm hoping my feet will toughen up, like Lex's, and I'll eventually be able to handle even cement well. I have a history of connective tissue problems, so it will likely take me longer to strengthen my tissues than most people.
It's interesting to see the wide spectrum of experiences here. Clearly we're not going to agree on a single perfect approach to every aspect of running, walking, brand of shoe, shoes vs. no shoes, or various surfaces that suits the current needs of all of us. Luckily, we don't need one.
Even though my speculative hypothesis is that forefoot-style is the most natural form of both running and walking, based on watching infants walk and anecdotal reports from and about some others, my feet so far have only gravitated to forefoot-style when sprinting or going uphill or up and down stairs (they naturally gravitate to flatfoot style or a very light heel-first style when walking on flat ground, even when I'm barefooted). My guess is that my feet will slowly gravitate more toward forefoot-style in the future, but I can't be sure of this. As I think I mentioned, I have also encountered counter-evidence to my hypothesis, in the form of images of traditional people walking heel-first in bare feet or flat-soled shoes and a video of a chimpanzee walking heel-first. The contradictory evidence is puzzling and it's an intriguing topic. I'm hoping that more evidence will make the picture clearer in the future, but in the meantime I'm enjoying the puzzle.