How do you determine what "needs" unit testing?
You aim for 100% coverage.
There are also advantages to Subversion that Linus states himself . Really the only one of note is that Git isn't so great at having multiple projects in the one repository and the recommendation is to have one per repository and have a super-project that contains pointers to others - which isn't so great a solution.
 It was stated in relation to the layout of the KDE repository: http://git.or.cz/gitwiki/LinusTalk200705Transcript
Much of the excitement we get out of our work is that we don't really know what we are doing. -- E. Dijkstra