The forums here are littered with engine issues, but here are a few recent and randomly selected SBF engines that have had issues:
Ford Racing 427 burning oil
Ford Racing 427w tuning problem
Dissapointing year end with my Roush 427R
Cam Lobe Pictures, Need Analysis Help
Putting aside engines that have bad parts and/or bad combinations and/or bad assembly and/or poor installations, I'm going to guess that as a percentage, SBF's have about the amount of issues as BBF's. At least it's closer than most folks think.