I was thinking the same thing, there are fractional ownership deals [1], charter airline brokers [2], and of course air taxis [3] (which are not often jets but what ever).

I realized this evening when slogging southbound on Highway 101 in the Bay Area what I really want is something that attaches to my car roof with a big NASA approved docking connector on it (aerodynamic though) which when I call up the app schedules a Sikorsky Sky Crane to fly by pick me up out of traffic and take me to my destination.

[1] http://www.netjets.com

[2] http://www.rsvpair.com/

[3] http://www.garyair.us/