AFAIK, the P4 faced badly on jump-happy code, but this was not common enough to be a problem on the real world when compared to a PIII. It was also a power hog, that could barely outrun a snail if you didn't have proper thermal management, but that also doesn't means the processor is slow.
I should have specified perf / watt. Pentium M's came and cleaned up compared to P4s, there was a fair bit of time there when, excluding massive power hungry desktop monsters, a beefy laptop with a Pentium M could easily beat an average desktop with a P4.
And IIRC pipeline stalls on the P4 hurt, badly.
Oh and RAMBUS, I had forgotten about RAMBUS. That also hindered the platform.
