I use DM's Familiar and love it. I run three different campaigns and can't imagine not using DMF. Primarily I use DMF for reference (all creatures, spells, feats, etc) and for running combat & rolling checks (spot vs hides, listen, etc).
I originally took to DMF due to it's simpler user interface. It was very intuitive for me. Also, it isn't a character generator, so I didn't have that overhead I didn't want. I use eTools for character generation, and DMF has an import capability that works for me. There is also a PCGen import method.
Definately give it a try. The DMF message board is great as well. You can get any of your questions answered there. (
http://groups.yahoo.com/group/dmsfamiliar) And there is a lot of additional stuff & help available on the unoffical DMF site (
http://groups.yahoo.com/group/DMF_Unofficial_Fan_Site) you would want to check out too.
Todd, the author, is also very available. Whenever I've suggested new minor features, I tend to see them withing a month or so in a new release.
I think DMF is one of my best D&D related perchases ever.