I'm far from an expert but I'd say water them. I'm in Michigan so mine will see a long winter too. I put them in a north facing bay window, and tried to be skimpy on the water and they started to drop leaves and shrivel up. I went back to watering them normally, and they came back quickly and are still growing! I know they are supposed to go dormant over the winter, but it's hard to put them away now, when they are growing more than they did over the summer! So, I guess that's not much of an answer, but I don't think letting them get shriveled up is a good idea...

Actually some shriveling is normal. They will plump back up in the spring. People have a tendency to overwater but that usually leads to rot. Some folks give maybe a cup or so a month, but I wouldnt do too much more than that. An occassional misting would not hurt either. Remember dormancy is triggered by reduction in watering and shorter days, etc. In their native environment they go dormant in the DRY season, which corresponds to our winter here.
Check out www.theplumeriasociety.org for information of overwintering and storage. Hope this helps!
Randy in Savannah

Thanks for the replies. I think I will go the cup a month route.....I'm bad at watering the plants I bring indoors anyway, so I don't think I will have a problem with rot.....lol

So am I doing the wrong thing by giving them sun over the winter? They seem to be growing so much better than they have been over the summer... I hate to stick them in the basement! Am I hurting them by allowing them to grow in the winter? I guess I am planning on letting them just go dormant when they decide.. is this ok?

Alecp-The only real danger of letting a plant grow in the winter is if you expose it to freezing weather it is very weak. New growth is the most fragile. If you are keeping them warm and inside, no problem. They will go dormant if and when they want. Make sure your light is not on all the time as the plant will need some darkness to release chemicals and be healthy. Water lightly until all leaves drop and then cut to a cup a month to keep the roots slightly moist. Bll

Hi Bill,
if temps keep cool where I live, don't plants inside get buggy?
Karen B.

Hi Karen- I am the wrong guy to ask on this since I do not bring my plants inside (with over 250 my house would be...they wouldn't fit.). You have a colder climate than I do so I can put the young ones under the patio and porch covers and the big ones in the ground are one their own. Since the 1990s I have only had two times that were cold enough and last year was the only time I lost plants and had to cut back four years growth on several. ( But I do know that inside plants get spider mites but maybe Karyn knows a treatment.) I have thought about cementing in foot long pieces of three quarter inch PVC pipe on the four corners of each planter and then inserting 10 foot conduit and then clamping clear plastic sheeting to the poles which would stop settling frost. However I just had major surgery and cannot do any heavy work for 2 months so this idea will have to wait. I may be able to experiment with my young nursery area but I am concerned with our Santa Anas which could blow my invention to Catalina. It is no easy solution. Bill