By tweaking some caching settings, a rather spectacular speed increase for loading a block chain was obtained. This will probably end up in 0.6 still.
I pulled #964 for 0.6 this morning.I had played with database settings several months ago and saw no speedup because there was another bug causing a bottleneck. That bug was fixed a while ago, but nobody thought to try tweaking the db settings again until a few days ago.
Pieter and Greg did all the hard work of doing a lot of benchmarking to figure out which settings actually matter.
PS: the database settings are run-time configurable for any version of bitcoin; berkeley db reads a file called 'DB_CONFIG' (if it exists) in the "database environment" directory (aka -datadir).