firstly great plugin!
i'm trying to use it with wpmu but realized a slight problem - wp-print requires you insert php code. as such i would have to manually insert said code into each theme. Thats ok for me because i restrict the number of themes - but for others this could be impossible.
in your next release can you implement an auto load option for various templates?
as a makeshift solution i was gonna use a prefix suffix plugin and stick the print code in there. kinda ugly way to do it
just a suggestion... :)