To eav or not to eav: this is a database question that comes up regularly (it's almost a FAQ).

Often, eav is advised against; here are a few links (with strong opinions -- against):

http://tonyandrews.blogspot.com/2004/10/otlt-and-eav-two-big-design-mistakes.html

http://decipherinfosys.wordpress.com/2007/01/29/name-value-pair-design/

http://joecelkothesqlapprentice.blogspot.com/2007/06/db-table-design-question.html

http://en.wikipedia.org/wiki/Inner-Platform_Effect

Update: (as a reaction to the "sharp tool" nonsense below):

I think it's fair to say that using EAV is almost always a beginners error.