Biking is suppose to be good for knee health. You're right to question my desire. The unspoken charge answered with a guilty plea. Then there's the cost of the bike, helmet, gay clothes ... etc. But yeah, bike riding be of great benefit. I'll keep an eye out on CL.
EDIT: BTW, which one is it that Greg likes? Is that what you got? I'm obsessed with health after eating pizza, chocolate and ice cream last night. I think I might be starting to see the problem.
There are tons of good brand name bikes on CL for relatively cheap. The big thing is getting properly sized. If you don't mind, pick a brand you want to explore, go to a real bike shop that sells that brand, get sized, then keep an eye out on CL for bikes that brand and size. You don't need clothes, but I do recommend a few things.
First, either a padded seat or padded bike shorts that you can wear under regular shorts. Either way, spandex is your friend. If no spandex, then extended rides are going to cause a lot of chafing and boxers/underwear turning into thongs. Not pretty.
Second, definitely invest in a simple bike tool and extra inner tubes to be carried with you on rides. Even a short couple mile ride can turn into a nightmare if you pop a tire with no spare innertube.
Third, to go along with the spandex, a shirt like an under armour material type material if you don't have one. Cotton, summer, and bike riding are a big no go IMO.
You may never get to this point, but I also highly recommend clip in bike shoes if you ever get comfortable enough on a bike for such things, but that's a ways down the line at this point.
The one that Greg likes is the one I
mentioned. They're pricey, but he's definitely right, but they are excellent bike racks. As someone who's owned a couple different types, albeit all that mount the bike using the top tube, I hate them.