I would like to see the capability to have multiple friends lists, say 3 to 6.
I use use the custom filter capability almost exclusively. I have a lot of filters (now, too many to easily manage). This is because the degree of filtering that I use for any particular email depends on what "group" I consider it to be in: Good Friends/Family, Work, Normal, Caution.
For example, currently I do not put any "Caution" email in the Whitelist, however, I also don't want to place them in the Blacklist - so it is sort of in the twilight zone. This email category often comes from exploder lists, which anyone may send to.
It would be much simpler for me to filter based on category. Each known (permitted) email would be on one of the lists. The filtering would be applied to the list. This would take care of ~95% of known email. I would still use my current filters against unknown email, and the Blacklist would still apply (although it is less effective nowadays).
AndyB