The kid's finally getting over her first cold, which has produced several sleep-deprived nights for all concerned. With a stuffed up and/or runny nose, she had a really hard time getting to sleep. Several times, she even seemed to panic a bit (understandably) at the prospect of not breathing. She'd always calm down and fall back asleep on our shoulders, but it wouldn't last.
Finally, at 4:30 one morning, we tried putting her in her car seat, so she could breathe a little easier, and it worked like a charm. No one recommends putting a kid to sleep all night in one [update: see comments. And of course, we let the kid sleep for 10 hrs on the flight to Japan.], but for a couple of hours comfortable nap, it's apparently fine. In fact, she's asleep in it right now.
Another thing you can do for a stuffy nose is get some saline (Little Noses makes one) and a nasal aspirator (or 'snot sucker'). You squirt some saline into their nose, just a little, and then use the sucker to get out what you can. It really does work....
Actually, my pediatrician did recommend that we put Everett to sleep all night in his car seat when he was really stuffed up. It worked like a charm for us, too.