Temporary directories getting errantly added into trees

I just got through a rather nasty debugging session with git-rebase,
which relies on a .dotest directory.  Turns out that .dotest was
accidentally added to the tree in the history of the commit that was
being rebased onto.

There are a lot of temporary files like that made by various scripts -
eg, git-filter-branch makes .git-rewrite, etc.

I think it would be a good thing for all if you had to work very hard to
put files like this in the tree, or perhaps it would be better to go
through and make all the tools that create these temporary directories
create them under .git instead.

Thoughts/comments?
Sam.