I recently installed phpGraphy - it is GREAT!! - but my VPS has limited memory so resizes using convert kept failing due to insufficient memory for large files.
By adding "-limit memory 100 -limit map 100" to the convert arguments it now works for low memory server configurations (limits chosen arbitrarily).
It might be worth adding something like this as a config option, although I'm not sure how many people would every try running it on such a low spec'd server.
(sorry if there is already an option in there/documented somewhere - I couldnt seem to find it)