What I dislike the most is the freezing-up-when-creating-a-new-folder-bug. Haven't bumped in to it lately tho.
I've lost about a days work because of this already (only had my mpc for a couple of weeks). Having lost work because of the "wrong file error" bug, I try to save the entire memory contents in a new folder everytime... only to witness the machine freeze as I try to create that new folder. Between those two bugs, there currently seems to be no foolproof way to regularly save the project you're working on. I think this is ridiculous.. on my computer I haven't lost a thing in years because I'm saving every minute or so, on the MPC saving is so convoluted I fail to do it regularly. I love what the MPC is doing to my creative workflow, but I would never have guessed a hardware unit to be more prone to data loss than software...