If you are not interested to use the CVS program for directly accessing the latest GRASS 5.3-cvs source code, you can follow ongoing development by download a source code from here. This CVS snapshot is the source code checked out from CVS experimental tree (HEAD) repository once a week.
If you are interested in very latest code, please access directly the CVS server for latest GRASS 5.3-cvs sources.
From time to time regular "GRASS 5.x releases" will be officially published.
Note: The required space for a full compilation is 340MB (including object.files etc). The resulting binary package size is between 60MB and 100MB depending on your platform.
Improvements and source code pieces are very welcome!