I think you've answered your own question. :) My memory is that it was rare pre 1998 in Silicon Valley but ubiquitous post 2005 or so - Silicon Valley and Seat

I think you've answered your own question. :) My memory is that it was rare pre 1998 in Silicon Valley but ubiquitous post 2005 or so - Silicon Valley and Seattle. It's unclear whether Seattle's development was independent of the Valley's, stemming from Microsoft's well known emphasis on algorithms and the same stupid logic puzzles that Google became infamous for.