For an initial comment, the same security restrictions that apply to
GRDDL http://www.w3.org/2001/sw/grddl-wg/

1. use of document function - can be used to read local files that you
might not want accessible.

2. use of extension functions in your processor that can run other
type of code - example msxsl script - but you don't have that problem

3. maybe XML security problems, stuff like external entities
http://www.securiteam.com/securitynews/6D0100A5PU.html I would suppose
libxml handles this well though, but have not done research on matter.

By the way I need to sort of do the same thing in a project I am
building. Would you like to discuss this further? I'm going to be
offline for the next couple weeks starting tonight so if you say yes
tomorrow I can't reply for a bit :)

Cheers,
Bryan Rasmussen

I was wondering if there were  any security considerations with allowing users
to upload their own XSLT?
I'm using libxsl which seems to guard against infinite loops etc.. but i was
unsure if there were other things which I should consider from a security
pov.

thanks in advance
Andrew