Maybe also keep in mind that this might annoy people ("my laptop freezes when accessing your page" etc.) and cause you a lot of support work.
I've spent some time to make sure that this doesn't lag your computer when it's in use. I've had several people tell me that they didn't realize when it was running, because it was so good at staying in the background.
This is based on my regular browser bitcoin miner, which was meant to be left open all the time on a computer that was in use, without getting in the way.