Single hung windows suck IMHO. The house I have that were trying to sell has a set of original 1927 single hung, with a nice storm window setup put on probably 15 years ago. They are lose as can be, you can actualy rattle them when they are latched, weather stripping? Whats that. Sure they lasted 90 years but they are lose as can be and leak a lot of heat. Plus you have to strip and repaint them, I don't want to do that or pay for it.
If I was keeping it I would replace them with some vinyle double hungs.
If you want a good wood window and don't mind spending some money, Marvin's are pretty nice:
http://www.marvin.com/?page=double_hung
Thats like something we would use if we were building a million and a half dollar house.