Recent Postgres major releases have been packed with features (9.1, 9.0), but you might have noticed a lack of major performance improvements in those releases. I was starting to think that we had basically addressed all the performance improvements we could.
Well, I was sure wrong. Postgres 9.2 is going to have a boat-load of performance enhancements. The inclusion in Postgres 9.2 of index-only scans and count(*) optimizations clearly is something that is going to help a lot of work-loads.