As well as having twitter lists would really like the customisation of the twitter follow service to receive push from spesific accounts. For example you typed in the name of the person you wanted notifications from into the app, you could then choose whether you wanted their statuses pushed or their whole timeline and you could choose a different sound for each user you wanted notifications from
-- As requested by Shan
Did you try the Boxcar list feature ?
It is described here:
You can select the users you want to get notified by putting them in a Twitter list called "Boxcar". Would that help ?