Neither do I!
It all depends on how those PIF are distributed over the disc. If they are evenly distributed I hardly care. If there's a narrow PIF cluster of 1000 PIF it goes in the bin, however!
A bad Read Transfer also goes in the bin, regardless of how few PIE/PIF the scans show.
If I get a disc with far more PIF than other discs from the same batch, I throw it away based on the theory that it might already be degrading.
I have media that cannot produce less than 3000-4000 PIF per disc regardless of which drive they're burned in, and they show absolutely no problem in Read Transfer tests or playback tests, and when scanned at 12x (maximum speed) in my Plextor PX-712 they scan better than most other discs that have nice low-speed scans!
You're welcome to trash discs with > 2000 PIF, but for me the keep/discard decision is more complex than that!