Two immediate problems with the formula and one problem with the concept.
First, "scope", factor 2 in the formula, can be external to the employee. It's in Spolsky's interests to hire people who "could" manage multiple projects if given that responsibility, but the demand for those people inside Fog Creek will tend to be lower than the demand for lower-scoped responsibilities. His formula thus does one of two things: it incentivizes him to hire less talented people --- even when he may want a buffer of talent inside the company --- or it creates a totally subjective ranking system where 10 people are qualified to lead a project, but only the "favorite" does.
Second, "skills", factor 3 in the formula, is also subjective. That he's coded it in a chart doesn't change the fact that the "skills" spectrum is basically the line over which every salary negotiation is fought anyways.
Which leads to the general critique of this, that coding and regimenting salary negotiation does nothing except code and regiment salary negotiation. OK, so Fog Creek is transparent about the behavior they want to incentivize. But so what? The real world still creeps in and subverts this system:
* "I'm capable of leading this project, but I'm never getting a lead role because 5 people with seniority are always going to take the next available slots."
* "I was given this task to complete, but it was poorly specified, and so my output didn't contribute to company success."
* "You'd be ranking me at a higher skills level if you put me on a project that would give me exposure to new technology."
* "You'd be ranking me at a higher scope of responsibility if you'd just recognize that my team lead is a moron."
All the same pathologies seem to remain intact in this system.
Curious as to what I'm missing.