It should also be possible to do efficient *estimated* COUNTs (using reltuples [1, 2], provided the DB can be regularly VACUUMed + ANALYZEd (postgres-specific awesomeness)) - i.e. if everything is set up right, doing COUNTs would be efficient. This would be nice not only because one could run very quick queries asking e.g. "how many consensuses include nickname LIKE %moo% between [daterange1, daterange2]?" (if e.g. full text search is set up) but also, if we have to resort to sometimes returning an arbitrary subset of results (or sorted however we wish, but the sorting being done already on a small subset of results, if that makes sense), we'd be able to also supply info how many other results matching these particular criteria there are, and so on. The usefulness of all this really depends on intended use cases, and I suppose here some discussion could be had who / how would an Onionoo system covering all / most of all the descriptor+consensus archives and hopefully having an extended set of filter / result options be used?
[1]: http://www.varlena.com/GeneralBits/120.php [2]: http://wiki.postgresql.org/wiki/Slow_Counting