from http://beneficialmanifesto.org...

important:
    good keyboard, at least 17,5x16,5mm
    umts, WLAN, LAN, Bluetooth, USB
    weight < 1,5kg
    Linux
    Expresscard
    VGA with different resolutions possible
not so important:
    big HD
    Display 10''
    battery time > 4h
    modem
    card reader
    mic, speaker
    webcam
unimportant:
    color (design)