Costco has a GV and a Challenger, I see them at BFI, RNT, and PAE all the time. Paul Allen's BFI hangar has 2 757's, a Global, a GIV, Twotter on Amphibs, Challenger, and some helicopter. Nordstrom has a challenger at BFI, Bill Gates keeps his Global at BFI, a big engineering company (forget their name right now) has a GV at BFI. MSFT does not have a flight department.
If you want to fly corporate floats, usually Beavers, most of those guys are out of RNT.
Like Ziggy says, little to no movement at the corporate gigs, just like QX in the airlines.