Gobby
Gobby is a free, collaborative text editor. See http://darcs.0x539.de/trac/obby/cgi-bin/trac.cgi
Collaborative text editors are cool on there own anyway but I was thinking about note taking in lectures. Its simple enough to setup an ad-hoc network between all laptops and then use one instance of Gobby for note taking. Guess that depends on how good it really is at keeping parts written by different users apart. Does it have LaTeX support?