Inactive Members
 

I think a hack should be made so you are able to delete inactive members who have been, say, a member for more than 60 days and haven't posted.

I've tried using the promotion system but it's not working out for me.

Agreed. There's a few hacks I've seen that show me who are the most prolific posters, but I'd like an easy way to see who's inactive or lurking.

I'd like to see, for example, who hasn't logged in, or who hasn't posted in 60 days, or "who logs in every day but hasn't posted in 30 days."

As of now I can delimit searches by "last login is before..." or "last post is before..." but it's very rudimentary and doesn't track activity and daily logins over time.

this is very easily done in your acp without a hack.
go to Admin cp >>> Users >>> Prune/Move Users >>> clear the 365, then where it says Join Date is before, set that to a date 60 days earlier, and where it says Posts Less Than, set it to 0 or whatever you want. then click on Find.
Check over the list of members, uncheck any that you don't want to delete, tick the delete, then hit Go.

you've pruned your inactive members ;)

There is also a hack available, by Andreas.