I'm in the same situation with the OS X client. I was using BTSync + Arc to essentially match Dropbox's feature set, but in the past couple of months BTSync seemingly lost its mind with respect to CPU usage. It would routinely hit 100% and would always show up on OS X's "Apps Using Significant Energy" list. I had to shut it down so often that it ultimately wasn't worth it. I switched back to Dropbox and abandoned any sort of privacy once again.