We've actually been working on something like this for San Francisco (and we plan to expand onwards after operating here): http://www.takehitch.com
The municipality tends to work a little slower here (chatted a bit with SFMTA in the past), so we're starting with a model that just focuses on private cars. But the fundamental point--dynamic re-routing to create custom routes where people can ride in the same vehicle--is very much in the spirit of what we're doing.
How do other Bay Area county/city systems match up? E.g. have you tried making a similar arrangement with AC transit and was/would it have been easier or harder?
We haven't, but that's a great idea. There are some limitations that tether us to cities (so networks like SamTrans in Palo Alto aren't ideal), but AC in the East Bay would be an excellent fit.
Response has been really good (a subjective answer :)). For more objectivity, we've received ~40 leads for one CL post, and got about 10 leads in small little twitter campaign ($5 ad).
People seem to be genuinely excited about collaborative consumption, and we enable route-sharing (I hesitate to use "ridesharing" since the term has become overloaded and isn't accurate to its origins). Passengers are sharing their ride with others, and that's new in the on-demand era.
There have been plenty of mental models built up with the one-to-one sector though (one driver, one customer), so we have seen the need to start explaining from the ground-up, so as to articulate the differences.
The municipality tends to work a little slower here (chatted a bit with SFMTA in the past), so we're starting with a model that just focuses on private cars. But the fundamental point--dynamic re-routing to create custom routes where people can ride in the same vehicle--is very much in the spirit of what we're doing.
We're still in a pre-launch phase, but check out our iOS app: http://www.takehitch.com/download