We've had it at 58 - 60 at night, sometimes we put it up during the day. R is a very cold baby -- he hates getting undressed & cries & shivers all the way through, so I keep him in two sleepers most of the time and almost always have him in a blanket (unless he's in the wrap). Even when the temp was warmer (we had a few days where it was close to the 70s) he was cold. He seems to be more comfortable now; he has gained 4 lbs but only grown a couple of cms, so he's quite round and chubby. It seems to be helping.
Now, my older kids on the other hand don't seem to be phased by the lower temp. I have to beg & plead to get them to put on pants (instead of shorts) and socks or slippers. I wouldn't really care, except they are getting over colds and I cannot believe the amount of mucous they're producing. I find being warmer helps, but they just keep dressing like it's summer.