Oh... something I forgot that bears mentioning.
I know that the rules were based off the D20 Modern SRD, and are geared toward that particular game, but it would have been nice to see some discussion on how the system would work with other D20 games. This is something that has, in general, been bothering me about 'house rule' supplements like this one...
Not just you, Keith, but most authors seem to forget about the modularity and variety of the D20 system. There are so many slight variations of the D20 rules for so many genres, and they are all compatable with each other to a degree. Those slight variations, however can make a big impact how many of the rules fit together. For example:
In Magic: The Science and Art of Causing Change one major drawback and limiting factor to casting rituals is the fact that the caster takes hit point damage every time he uses magic. Damage equal to the DC of the ritual. For even the most simple spells, that will be at least 8 or 9 points of damage when casting in combat. Playing D20 Modern this is less of a problem, since it is assumed that you cannot use magic until you have access to advanced classes after 4th level or so, and you have a significant pool of hitpoints accumulated. If you were to use this in any other D20 system, however, your typical 1st level caster would kill himself the first time he cast a spell.
A sidebar or two giving alternate suggestions for dealing with the damage in other systems would have been nice.
It also would have been nice to have a paragraph or two addressing how the system could be used in other genres. As I said in the review, if you shuck away the flavor text from the rules, the versatility of the system shows a lot of promise for sci-fi psionics, wuxia wire-fu, comic book superheroics, or any other super-human type of powers. Even without specifics, the very suggestion would broaden your audience.
My first thought reading through the PDF was, "This would be a great substitute for the crummy T20 psionics rules."