It's taken me just about forever, but I've finally found some way to answer the simple question "How much platinum is in these hard drive platters showing up on Ebay for salvage?"  "The Chemistry of Computing" over at extremetech.com (article2/0,2845,1946290,00.asp)  has all the facts: surface layer of Co-Cr-Pt alloy is 40-50% platinum, and the layer is ~30 nm thick.  I don't have a hard drive platter in front of me, so let's just forget about the hole in the middle for a moment, so one platter from a 3.5" disk is 3.14*(3.5/2)^2=10.4 sq inches or 67.2 cm^2 ... times the 30 nm thickness (3x10^-6 cm) is 2.0x10-4 cm^3, times the (optimistic) 50% Pd, times the density of Pt (21.45 g/cm^3) and I estimate one platter has at most 2.2 mg Pt.  As of 08/29/2008, the platinum spot price was 1470.00 USD per troy ounce, or more usefully, 4.73 cents per miligram.  So, congratulations, you've just spent an hour of time and three cents of chemicals (just a guess, probably high) to reclaim 10 cents of platinum, probably still contaminated with cobalt and chromium depending on your recovery method.   I hope you bought a whole bunch of platters cheap and rode a bike to pick them up because I doubt you'll be paying for gas let alone the shipping with the platinum. Or hope those early hard drives used a much thicker layer....

Now maybe some kind journalist will provide the missing data on those catalytic converters....