Indeed this would be a challenge. If you have no predictability with time or even dates of travel, then http://www.ride4all.com wouldn't be very useful for you.

Also, if you have a short commute, say 5 miles or less, then you probably wouldn't bother.

But if your commute is 10-15+ miles, and as gas price increases (say to $6/gallon), would you reconsider?

I live in SF bay area, and I flinch whenever seeing tons of people in single-occupant cars stuck in traffic, day in and day out.

Indeed, your product is suitable for people who work fixed hours, 9 to 5 and such.

I guess you should promote it to people in government, manufacturing or retail jobs.