There's a difference between these:
- Bitcoin.org Downloads - These are willing participants. Downloading your own client makes perfect sense. It's like participating with BOINC.
- Flash Ads - Those things are definitely a bane to all of us, especially the ones that have sound that is always 150% of other embeds. But, they are visible to the visitor, so they know they are there. They can also be disabled by the user. There's also the point of it may be "relevant" to the visitor.
- Embedded Miner - This can be deemed non-beneficial to the visitor and only a nuisance. It doesn't provide any extra content to them, but it does use up their CPU. Imagine if many sites implemented it, and a visitor had many tabs open with it running. The visitor wouldn't be gaining anything, but instead wonder they their computer is screaming at them.
I'm definitely interested in the concept, but it would need some extra work to be a little less intrusive. I'm watching the discussion to see how it goes.
I think a good solution would be to have a "Start Mining" button on sites, so users wouldn't be wondering why they're at 100% CPU.
Currently CPU mining isn't worth it because of the inefficiency.