When I attended my first and only knife show, the first thing that attracted me to a maker's table was their aesthetic. I usually only check out folders, because I don't think I'm too likely to carry a fixxed blade.
When I pick it up a knife, I notice how smooth the action is, and how well it sits in my hand. Some knives feel really at home in my hand, and some feel like they want me to put them down.
The thing I find most facinating about a knife is if it has some kind of cool mechanism. Speed-safe is one cool feature I love (thanks Ken). Aside from that, the nifty mechanism is usually the lock. At the show I went to, I got to handle a Lile knife (patented Lile lock), and a Paul Fox knife (button lock). I've also been impressed by the axis-lock.
I guess for me, if I were going to buy another knife, I'd look for something that offered a mechanism that was "simplisticly genius." I guess that's why since I just got my Mini-task, my next knife will likely be an Axis-Lock.
Sorry for rambling,
Mitch