In order to make UWSim easier to install and ready for groovy and future ROS distributions, we have created a 'catkinized' branch of UWSim and released deb packages for it. Now installing UWSim should be as easy as:
$ apt-get install ros-groovy-uwsim
This required to make some changes in the data package download process and its location. Now, the first time you run UWSim it will download and install the data package under ~/.uwsim. The --dataPath argument should be working as before in case you want to specify additional paths to resources.
For those of you already developing under Groovy and requiring the UWSim sources, you should create a catkin workspace as described in the wiki:
We will be releasing for Hydro and forthcoming distributions as they are released by the ROS community.
Hope this helps! please open github issues for any problem you may find.