Wouldn't you also be offering your machine up for hosting DOS attacks, piracy, child porn trafficking, and other activities that would get you booted from your ISP?

It wouldn't be hosting it. It would be client-side, and if it's http over ssl rather than tunnelling DOS attacks would be difficult.

Excellent repurposing toward accessibility, C.D.

Now if we only had some mechanism to prevent outages due to too-many-retrieval-requests, like some kind of distributed universal caching/mirroring thing... we'd really be cooking!