I've been pretty hard on my left knee over the last 26 years. It started with a skiing accident at 14, then I fell down an icy ramp at 30, and finally in 2007 my foot slipped off a shovel I was standing on while digging a ditch in my backyard (yes, I can be very stupid at times). There were other incidents in between, but those 3 did the most damage. After the shovel incident, I had surgery to trim my shredded meniscus.
To this day my knee still acts up on occasion, and what aggravates it most is standing for long periods of time at work and gigs, working a hi-hat pedal, high-impact aerobics, walking long distances, and running. However, when I was in grad school I rode my bike every day and it never gave me a problem, even after riding for over an hour at a stretch.
When I quit riding about 10 years ago, my knee started giving me grief again, and this was even before my last 2 accidents. Then about 9 months ago, I started doing Tae Bo and it has really improved. I can definitely tell that it's weaker than my right knee and likely always will be, but as long as I avoid moves that require jumping or excessive twisting, I feel pretty good. I think that as long as you do something that strengthens the surrounding muscles (which includes biking, according to a former colleague of mine who was an athletic trainer), you'll be okay.