find ~ -type d -name .git -exec dirname {} \;
will show you all folders in your home directory which have a .git subfolder — i.e. they are git repositories.
This is useful, but can be extended to:
find ~ -type d -name .git -exec dirname {} \; | tr '\n' '\000' | xargs -0 -n1 -I % git -C "%" status
to show the git status output of all your git repositories.
Time to clean up!