re: "twitchiness"
this is a word that's use all the time to describe handling, and it feels seriously devoid of meaning. it doesn't help me understand other people's experiences with bike handling, so if people would be willing to use some other words to describe what's going on with handling, that would be great.

here's my experience. my pogliaghi has a tight, steep front end - pretty traditional track geometry (but with longer than usual chainstays). i expected it to handle "twitchy" since that's what everybody says, but i found it to be smooth and responsive instead. twitchy seems to be quick and unpredictable, but even with my pog's very quick handling, it's decisive, not about to respond unpredictably.

i'm not sure exactly what to attribute that to, except perhaps that there's the right balance between rake, trail, and angles - perhaps it's a little bit more stable considering the slightly longer chainstays, while being quick as anything with the tight front.

anyhoo, yes, rake and trail are interesting. i'd be very interested in hearing framebuilders chime in with some of the things they consider when they think about handling, bike design, and the way all of these factors interact.