LOL -- i *love* this forum!
cerulean, great question, and i found David's answer very thoughtful. my reasoning is different, because i have different uses for my knives than David does, but i come to a similar conclusion:
i like serrated blades for opening boxes, which i have to do a lot of in my job as head network nerd. the serrations make short work of fibrous packing tape, and also the weird grades of cardboard used to package computer parts.
when opening a box, i don't want a blade that is too long, or i risk cutting the contents as well as the tape or the cardboard. also, a longer blade requires just a tad more force (theoretically, right, more mass?), and with more force i run the risk of punching the knife through the box to the goodies inside. this is Bad (especially if the contents are your much-needed new memory chips for your server, right Spark?).
plain edges are for cutting my food, and opening mail, and other tasks where i don't want much carnage to result. trying to cut a sandwich with a tiny blade, well, that just don't cut it with me (ducking to avoid incoming rotten veggies).
so i also would vote for the shorter blade to be the serrated one, and the longer one to be the plain edge. (i'm not saying my reasons are really sound ones, they're just MY reasons, which i encourage anyone to talk me out of if you are wiser and more experienced with blades than i am.)
plus, i just don't like to scare the kiddies, and a long fully serrated knife would give my coworkers heart attacks, the poor babies. they're such sheeple that they get nervous when i pull out my pearl-handled BM 850!
due to being plagued by Stupid Girl Clothes, i don't always have two (or three) pockets for my carries. when i do, the shorter blade (which i use most often) goes in my waistband, opposite my strong hand, and the longer blade goes in my strongside pocket. (weakside pocket is reserved for my keys and multitool.) If no pockets are available, long blade get relegated to outside pocket or strap of The Purse, and short blade is clipped inside my armhole, to my blouse placket, hem of sweater, ear of flunky co-worker (oh no, wait, that's wrong) or anywhere else i can find.
i'm finding that i don't like my longer blade so far from my hand, however, so i'm working on a solution for the days when i have to dress like a girl but when i need to be prepared like a boy scout
silverwing