[Orgmode] Keeping org files under git - trimming the repository

[Ben Alexander]

Hello all.
This is really more of a git question, but I keep my org file stored  
under git and I've seen other people on this list speak of doing the  
same.  Different people cite different benefits:

+ keeping home and work copies of todo.org in sync
+ storing todo.org on a USB stick for transport instead of using a  
network
+ safety while editing. If a slip of the fingers hits C-k on a folded  
line and you don't notice it for a long time, git allows you to find  
when that happen (git blame) and 'cherry-pick' a patch to bring the  
lost subtree forward in time.

I don't really know how to do any of  these things in git, but that's  
what you all say :-)

About a year ago, I decided to learn how to write "macros" in lisp and  
started by teaching myself about the after-save-hook.  I added a hook  
to auto commit every time I saved any org file.  My simple, small text  
file of todo items is now a giant git repository.

At last a question or two: Does this happen to you? What do you do?   
What new git command do I need to learn in order to do it?

Is there some way to clone my git repo onto my USB stick, but make it  
a subset instead of the whole thing?  That would be useful for me to  
learn for other git projects!

Just curious!

(and thanks to you all for the interesting discussions and excellent  
tool!)

-Ben