How comfortable do people feel with the old push-downhill-and-jump-in technique for getting into carts? Powered tracks only boost carts already in motion. They won't do anything if you're sitting motionless. So, when planning stations or substations, we may need to account for building launchers.
And automated launchers are not small.
I've been trying to build a compact, sealed (to keep mobs and accidental miners out) launcher this evening, and here's what I've been able to produce so far.
Video:
http://www.youtube.com/watch?v=GwmFZ9ewxGU
FWIW, "diagonal" tracks ride fast and smooth and are not jerky as you might suspect. Also, tracks are a PITA to configure right. There are some pretty obnoxious alignment issues, at least when I've been trying in SMP.