"Try scanning at 4x - 5x, that's the standard, faster scans will show more errors."
On the 3540, actually one can scan up to 16X with reasonable consistency. These PIF peaks are not normal. Neither does this: "at aroung 70% of the burn but....the device buffer went down and stayed down for about a straight min. and the disc would not get past 4X at that point"
Have you checked the disc for scratches?
As for how to read the scans, Ricoman summed it nicely. On the NEC 3540, though, PIF single spikes may go higher than 4, about 6-8 and this wouldn't be a concern.