I've also noticed that the bitcoind JSON-RPC response times do seem a bit high, especially if running on modest hardware. But I've not investigated further.

I wonder how large scale bitcoin sites (e.g. satoshidice, mtgox) perform operations such as checking for transactions and making transactions - do they use:

• the standard bitcoind JSON-RPC interface
• a lightly patched bitcoind
• a heavily customised bitcoind
• a proprietary client that speaks the bitcoin protocol
• an application that bypasses bitcoind and pokes around in the bitcoind database directly
• a mixture of the above!