I really should revive the Sluice project. Keyword filtering and setting aside items are two of the most concrete intended features (alongside de-duplication and same-link post stacking).
I have to admit I was interested in exploring the social side with my app as well, so I'm glad Google made that mistake before I did. =^)
I just want a way to manage my river of news so that the can't-miss items aren't missed, and the always-skip items are skipped, and above all I should never be blithely offered the same exact link with the same exact metadata more than once. Everything beyond that is negotiable.
There's a lack of keywords feed filtering, feeds personalisation, items expiration, some way to archive items for later and on and on...
My guess is that it's a very small team working on Google Reader and that they have the wrong priorities : the social stuff, at least it is for me.