Knee injuries among racersI read a couple of years back that the number of torn ACLs among current World Cup alpine racers expressed as a ratio to the number of racers is greater than 1:1.
(That is, more of them have torn 2 ACLs than have torn no ACLs; each racer has, on average, slightly more than 1 torn ACL.)
Given that the ACL is merely one of many kinds of knee injuries (MCL, LCL, meniscus, other) and in addition to ligaments there are a bunch of fun tendon injuries as well (patellar tendinosis, anyone) its safe to say that almost all ski racers have had one (and probably more) knee injuries if they've raced a lot of days for a lot of years.
That said, speaking from experience, (1) the older you are, the longer it takes to heal, and the longer the pain seems to last, (2) Bode Miller is a phenomenal athelete, in phenomenal shape. If he's skiing hurt and functionally loses about 10-20% of leg strength in one leg because of injury (as he did one of the last two years--by the end of the season, one of his thighs was much smaller than the other one, and he was quite frank about it) he can still ski at a high level. For us older guys, losing some functional strength to injury really makes much more difference, because we don't have enough left, and (3) if your knee issues are irritation/overuse ones (tendinosis, etc.) you just have to pick your spots, and running enough gates to qualify for Nationals may not be in the cards for someone even as gifted an athelete as Phil's brother Steve.