I think Up the Duff is excellent when paired with something else of more substance. I'm very attached to Sheila Kitzingers, Complete Book of Pregnancy and Childbirth but enjoy Up the Duff when I just want a bit of easily digestible info or a giggle about whatever physical/emotional changes are going on. Up the Duff also stands out for me because it uses very careful language and never assumes that you are partnered or that your partner is a male. I think this is the downfall of even the more progressive preg/birth/parenting books. (All the Sears stuff is particularly bad for this!)

I also have Birth Your Way (Kitzinger) and am really looking forward to getting into New Active Birth.