I've used this guide to successfully get a complete copy of wikipedia offline.
Oh rad, thank you. I've looked at lots of different approaches but haven't seen that one. Looks efficient... I think you can get lzma wikipedia files now too, which saves quite a bit of space.
i've seen the following versions: kiwix (interface), moulin, one for iphone, OLPC (based on iphone version, plus they have good wikipedia scrapers), mokopedia (for openmoko fones--uses lzma squashfs), and probably others.