Here's one for the @b0rk compendium of git oddities.
Today I learned there is a difference between a lightweight tag:
$ git tag v0.20
$ git cat-file -t v0.20
commit
and an annotated tag:
$ git tag -a v0.21 -m "this is an annotated tag"
$ git cat-file -t v0.21
tag
I have only ever used the former, but it's possible for software to care about the difference between the former (the type of the object is commit) and the latter (the type is tag).
