Maybe it doesnt scale too well for sites as big as davout`s sites
It was what made Instawallet absolutely unusably slow in the beginning of 2012.
I used to use it for Bitcoin-Central as a second layer of accounting, but at some point I realized discrepancies, which were due to the silent rounding.
Anyway, I don't mind this feature, but I think it's going to be really great when bitcoind uses a relational database that you can query directly.