I have used Mears a few times to get over to Universal. Last time I used it, I was the only one being picked up at the time, so they actually sent me over in a taxi. On the way back, you call a couple hours in advance to arrange your return time.
Just a note, though, plan on it taking about an hour (or more) to get back to your resort. Every time I've gone, they have picked up people at Sea World, and then dropped off at several resorts (both on and off Disney property). I always seem to be one of the resorts that are dropped off in the middle with a few more stops after me and it seems to take about an hour.