Everyone has always used index cards, right? Well, not exactly. Levenger (see an upcoming book review of Steve Leveen’s book - a quick read with great advice on reading) has a brief, interesting history of index cards (found through 43 Folders).
Speaking of 43 Folders and index cards, check out this Hipster PDA. Found at 43 Folders. I’m still sticking to my PDA, but one of these days I’ll post my way of using a 8.5 x 11" sheet of paper for a similar purpose.