I've had fast ORD transits and slow - it depended on

1) time of day and node loading (many int'l. flights arriving or few)
2) distance between arriving gate and immigration queues
3) length of immigration queues
a) for visitor queues, often origin of arriving flights impacts queue movement
4) efficiency of baggage delivery system
5) length of customs exit queues (but see dstan's remarks - go right)
6) number of pax waiting for train
7) queue length and disorganization at T-3

I try to shoot for a two hour minimum connection time international to domestic at ORD - "stuff" often happens at ORD, particularly weather, ATC holds and schedule stuff-ups (especially as the day progresses.)