Used it today. Sadly, not much to report -- my driver was as curious as I was ("Looks cool!") but we didn't get routed to anyone along the way, so I just had a normal Lyft experience (but free).

Driver brought up a great point though -- there doesn't seem to be support for specifying how many people you've got to travel (or is it designed just for a single person?). He said he could foresee stopping to pickup a second passenger only to find out there were 4 people in the group (and not enough space.)