A *much* awaited feature, this attempt at adding the GROUPING SETS / ROLLUP / CUBE feature to PostgreSQL has been in the works for about a year (besides the so many in the past decade and a half that didn't get through), and thankfully this has finally got the approval of the powers that be, so the upcoming Postgres 9.5 would finally have this long pending SQL feature.
MSSQL and Oracle have had this for a while and then its time that PostgreSQL sport this as well. A big boon for Report generating SQLs this feature basically makes (what was earlier possible with lots of unmanageable hack of SQL), now possible with much cleaner code, and with much better (at times single pass) performance.
Read here to know more about OLAP support in PostgreSQL.
Thanks a ton Andrew Gierth and Atri Sharma and so many others who directly or indirectly assisted in getting this patch out of the door!
Andrew / Atri... take that long pending break... one look at that mail thread and it seems you deserve it :D !