The Tramvia (or Tram) Line 1 (from Santa Maria Novella to Villa Costanza in Scandicci) is nearing completion. I think this is going to be great for Florence - but line 1 is definitely more of a commuter than tourist line. Hopefully it will be operational in early 2010. Whether the rest of the line as planned gets finished (around the Duomo and Piazza San Marco, etc.) remains to be seen - but this has been a huge project and it will be fantastic to see this thing working after all these years. Below is a map of line 1:
More info can be found on these websites: www.tramvia.fi.it and www.muoversiafirenze.it.