I think the trolleys run until 8 pm. There has been a huge increase in ridership given the state of the economy. It's not the most convenient way to travel, especially on the beach, but it will get you around.
From the airport I would recommend using it, especially if you're hotel/condo is on Front Beach Road or Thomas Drive, since that's where the route runs. If you're out and about during your stay, though, you might want to call a beach taxi service... lots of times you can go from place to place for $10. It's better than waiting for an hour for the trolley.
Service on the beach seems to be a little slower (about an hour in between runs). Fare is in the $1.25 area. Or you can buy a monthly pass for $15 if you are going to be here for a few days.
Hope that helps!
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