thanks for the answers so far- i checked mine initially by drawing a line on a long sheet using the backside of the rail as a ruler, then flipped it around, matched the the ends, and drew again- it resulted in a "football" shape, showing 2X the deviation. the bend was actually a bit under a 1/16", but this little bit made it semi unusable for casework.
i designed a modular RTA furniture system a few years back that was based on a proprietary extrusion profile we drew up, so i got way in to tolerances, intricacies, etc. of aluminum extrusion during design, prototyping, manufacturing. i saw that in some cases, to get extrusions to really tight tolerances you need to get in to post extrusion machining. but with a big buget, you might be able to get around this.
my main interest concerns whether or not the guide rails always do as most extrusions do- approximate a straight line with a given tolerance. if it is always a matter of degrees with these things, one could end up having a hard time continuously getting square sheet components using this system. basically is it always a matter of degrees or can you really reliably emulate a panel saw for making cabinet parts?
certainly the saw still has a zillion applications even if the rails tend to be, say, 1/64th or 0.5mm or so out of line, but it would be nice to know that QC only approves rails so straight you can really do anything with them.
(since i don't have the saw on me i haven't been able to further check all this out...)