Mileage waitlist do come in occasionally. Flying from FLL the Tuesday after Thanksgiving, I was told ahead of time that I had a good chance of an EUA, so mileage waitlisted my wife. Well, of course, she ended up in F while I sat in Y. That said, much of it depends on the route. I've had no luck at the transcon routes like EWR-SFO, EWR-SJC, EWR-LAX. In each case where I've been waitlisted and not gotten the upgrade I've 1) had to call CO to get the miles redeposited after the flight and 2) had to call the elite desk to get un-waitlisted in order to do OLCI. (The elite desk person has sometimes told me that I shouldn't need to do that but if I basically act like an idiot with an idea fixed in my head, they eventually do it and then the OLCI that failed before the call works, as if by magic.)

Being as I'm only a few miles from EWR, I'm pretty much stuck with CO unless I want to make lots of connections. That said, I've been pretty happy with their service except for their computing systems. They should be able to redeposit miles automatically, allow OLCI while still on the waitlist, determine whether the upgrade would have happened via EUA and, if so, redeposit the mileage, and notify me of major flight delays early enough that I could have sat on the beach at NAS for a couple more hours instead of spending them in rainy FLL when there were major delays at EWR. (I can dream, can't I?)