If anyone is interested in tracking adoption tomorrow, my employer released a real-time counter showing adoption by % of web traffic (obviously a sample): gosquared.com/yosemite.
How many of those users are still using Safari 5.1 (as opposed to FF/Chrome/Opera)?
PS: It's even weirder that people are still using Lion when apparently any Mac that runs Lion can run Mavericks (and 10.9 in my experience is much more stable than 10.7).
I think it can run 10.7 unofficially, but it requires a little bit of hacking.