If I've booked directly with the hotel I bring a hard copy of the reservation info and don't bother reconfirming, but if I've booked through hotels.com or similar and I know there's enough activity in the area that free rooms will be very hard to come by, I will contact the hotel 2-3 weeks ahead of the date to confirm directly with them...I'll usually end up with their reservation confirmation number, at which point I figure I'm in "suspenders and belt" territory.

The only time I've ever had a problem was when one hotel said they couldn't give me the room/bed configuration I'd requested because reservations were just "recommendations" and not guarantees, but we worked things out - and it wasn't as if there was no room available at all.