I buy all my cels online so, my keep track system 
is an email folder with all the emails relating 
to cel orders, and discussions of cels I finally 
purchase. 

Soooooo cumbersome! Especially when negotiating a 
price etc with someone, I get 15 emails relating 
to one purchase/sale. Your use of a spreedsheet 
is far more elegant. (He says opening excel 
up......)

I think keeping track is a really good idea - I'm 
sure everyone does to some extent even if it is 
all "up in my head somewhere".