Yes, I've heard of problems. Just today someone said that Log and Transfer didn't work properly...kept crashing the system.
There have been reports of it not launching, exporting out of sync...saying CODEC NOT FOUND when working with XDCAM. How far ranging is that? Dunno. We only hear about the problems on the forums, not the successes. If you sat in the waiting room at a hospital you'd think everyone was sick, that there was some sort of pandemic.
I do know others that have reported now issues. But it all depends on what part of it you use...I guess. The OS wasn't designed for FCP 7 in mind. If you must use it to earn a living, I HIGHLY recommend you install it on an older OS, or keep around the older computer that you have it installed on to revisit those projects.