Cute, but this is hardly worthwhile unless you have a massive number of users, in which case you probably don't want to piss them off by wasting their CPUs. I'

Cute, but this is hardly worthwhile unless you have a massive number of users, in which case you probably don't want to piss them off by wasting their CPUs. I'm getting about 13K hashes/sec with this JavaScript miner. For comparison, my GPU gives me 100M hashes/sec, and even my 12 CPU cores give me 10M hashes/sec with the official Bitcoin client. So you'd need about 1000 concurrent users at all times to match a single machine. EngineYard SHA1 contestants who used this approach had the same problem. Now, if Native Client was widely deployed, or you could somehow rig up WebGL...