With the thread about paint and a lot of people doing bathrooms, I thought I'd pass this along. It's from the Pratt & Lambert site and I think it's worth knowing as I've heard of people having this problem before but never knew the answer.
"We painted our bathroom 3 days ago and now we have these brown streaks running down the walls. What are they and how do we correct it?
The condition you described sounds like surfactant leaching. Surfactants are surface leveling added to latex paint to improve its flow and leveling. Under conditions of high humidity such as a bathroom these surfactants can sometimes leach out of an uncured paint film. It will look like someone shook a can of cola and sprayed it on the wall. Surfactants can be removed if you wash after they first appear with warm water and a sponge.
To prevent this from happening in the future you must allow enough time for the coating to cure out before exposing it to heavy moisture. By having a good ventilation system it will lessen the possibility of the stains from reappearing. Finally, alkyd paints do not contain surfactants so use an alkyd paint instead of latex. "