I have fairly recent experience with this myself. A short chronology:

February '11----fairly serious tear in what the doc said must have already been a torn medial meniscus. The loose end flipped but fortunately, didn't slip into the joint. . .was just painful.
April-- (five weeks ago) arthroscopic surgery to cut away the torn bits and clean up the rest. Iced it non-stop for the first few days, then most of the next week. No exercise for the first three days, then a series of exercises a PT friend gave me- - -stuff for flexibility and to maintain muscle to some degree. Was out of the office for a couple of weeks but if there were a critical need for me to be in, could have been back, albeit hobbling, in a week.
4 weeks ago: daily indoor stationary bike with no resistance; start taking glucosamine/chondroitin/MSM daily---forever for joint health (per docs instructions)
3 weeks ago: easy road rides of a about an hour. . .about every other day
2 weeks ago: up to five days a week---slightly longer rides
1 week ago: resumed commuting on mostly flat with a few hills 15-miles each way---back to daily riding of either commutes or 90-minute mid-day jaunts
2 hours ago: finished a short but satisfying (all things considered) 45-mile rolling Memorial Day ride

Since the 'scope' work, I've iced it on occasion and wear a compression bandage when it bothers me- - -and it bothers me more from extended walking than it does from riding. Doc says no running and no cyclocross but I can ride all I want. As I understand it, this isn't an injury that will ever heal itself. You have few choices---live with it (if you can and hope it doesn't get worse) or have surgery. Unless you're young and the tear is in the right place, it can't really be repaired (as in stitched together). But apparently the surgery I had (cleaning out the shredded bits) is extremely common and highly successful. So far, it's worked for me. As noted above, I rode 45 today slightly slower than normal (it was also in the low '90s) and feel fine.

YMMV.