Javascript Bitcoin Miner
It is bad to use a bunch of the user's CPU without any notice. They will probably notice that your site makes their computer slow and never come back again. Also, once they find out you've been using their CPU power/electricity/battery life surreptitiously for private, unshared gain, you will probably have some angry customers.<p>Additionally, does this automatically hook in to slush's pool or something? Bitcoin mining is practically useless on CPU; even the fastest CPUs out get way, way less than 10mhash. The average length of time to find a block at 9999khash and current difficulty is 1200+ days, so even that estimate is over-optimistic, so this isn't worth anything if your users don't sit on your site for 5 years+, unless it's hooked into a pool or some other contraption to pay on shares instead of blocks.