[VonKatzen]

Assuming that quantum computers and digital AI are not actually possible what limit does that put on computer Complexity ratings and software functionality?

For example, dumb programs can be brute forced to solve certain problems and cleverly arranged to solve other issues. But the more complex they get the harder it is to get the desired results and the more layers of error become possible (because no human being can possibly keep track of all the sub-systems of programs the program he programs is running). Likewise, brute-forcing is limited if you can't build computers that are way faster than modern computers (which may in fact not be possible, Kurzweilian predictions aside).

My initial thoughts are to put some limits maximum complexity as well as what skills a computer can possibly emulate (with Familiarity penalties for trying to use a computer to do something complex it's not specifically designed to do).

It also limits the utility of massive data storage and retrieval capabilities. The IRL NSA has already run into having so much data that you can't possibly find what you want unless you already know what you're looking for. With trillions of terabytes of trivial data this could make it actually difficult to use the 'internet' to find anything useful.

This actually opens up some more utility for PCs in Ultra-Tech settings (they can't use technology to replace verstehen-based problems, only narrow technical ones).

A Few More Thoughts:
If raw power has limits and there is no true AI then computers may be developed to be more elegant - more reliable, simpler, more specialized. They become easy-to-use or ultra-specialized tools instead of all-purpose rigs. This would also make hacking/controlling digital machines harder, as they'd be disconnected both physically and in terms of engineering.

Pyramid #37 has some alternate rules for computers that might suit this setting/assumption, too, since they don't really get into AI rules in the first place.