actually its more like 58. i know cuz i just got my new air yesterday and its the first thing i checked. the 80 is formatted down to about 72 and with osx and all applications it comes down to 58.
I got my installation of leopard down to around 6gb
Printer Drivers, extra languages, X11 etc.... all eat space for what is to most people no reason. Why do I need 3gb worth of printer drivers ? Chances are you only have 1 printer, not 180 of them
the real starting size will be ~ 74.4 GB (80*.93). A minimum install of OS X should take about 6 GB, as already stated. So I would think the most you could possibly have to play with when starting out would be ~68 GB.