I've used them a few times. They have an east coast, and a west coast repair center (depending on where you are sending your lens from). I have always used the west coast center, since I'm in Texas. Service has been good, and total turn around time has been a couple of weeks. With that said, I have read some complaints about slower service from Nikon over the past year or two.
So, if the lens is not under warranty, I would use
APS Photo Repair. I have used them, a couple of times in the past, also. Their service is excellent, estimates are free, and turn around time is also not more than a couple of weeks (usually less). Prices are on par with the Nikon repair center.
But, the big question is, what lens do you need to get repaired? All lens repairs are somewhat expensive (let's say $200 -$800). So if it is a "pro" quality lens, send it in and get an estimate. If it is a kit lens, I would just replace it with a new one.