The electric mini-buses that run in the city center had a radical change this year (2010) when more of the center was closed to traffic. The below map shows the updated routes: C1, C2, C3 & D (don't ask for the logic on that - "C" must mean center now... but why the bus on the other side is "D" and not "O", or why they didn't keep A, B, etc... who knows!).
You can also see the Tramvia Line 1 on this map.
The buses run Monday to Saturday, from 7 AM until 9 PM, every ten minutes, and 8:30 AM to 8:30 PM on holidays. I guess they don't run on Sundays - which I had not noticed before.