I use the following command to convert a pdf from CMYK to RGB - I dont have access to the generation of these PDFs. The reason I'm doing it is so that the colours look correct on an iPod device.
ps2pdf -dPDFSETTINGS=/screen -dOptimize=true -dUseCIEColor some.pdf converted.pdf
When I run this there are some white lines that appear and the fonts on some parts of the page are messed up. These problems are not present on the source pdf files.