The Tram is now complete which goes from the Dubai Marina area to Jumeriah. You can use the tram to connect to the monorail for the Palm Jumeriah and the shopping center next to the Atlantis hotel. So the metro system is definitely growing.
There were plans to extend one of the main metro lines past the main airport downtown (DXB) to Academic City by 2018. Those plans were apparently put on hold to focus on extending the line in the Jebel Ali area (the other side of the city) due to the World Expo 2020 being held there. Dubai’s new airport, DWC, is also located in that area with talks to have the metro line stopping there. That would be great as only one bus route currently goes to the new DWC airport.