Ready! :-D

See for example:
https://steemnow.com/@ocdb

It starts adding up SP after about 10 seconds. The script first needs to make some calculations after a few blocks have been added to the blockchain. After this short delay, the amount of Steem Power is updated every 3 seconds (with every new block).

All calculations are made on the client side, so it does not burden the Steem node every 3 seconds.