Features most important in a MIDI sequencing program

What features would you (or do you) make use of in a sequencing application?

MIDI input/output

VST or other soft-synth technologies

ReWire

Multi-channel audio input/output

MIDI file import/export

System Exclusive messages

Which editing styles/interfaces should be included?

Piano roll

Tracker

Event list

Score

Would you prefer to set up your sequencer once according to your equipment setup, and then be able to use it, or would you prefer to set up each song differently? (In terms of patch lists, initialisation, etc.)

Set up once per installation

Set up once per song