Over at Metafilter, in an unrelated post, someone named yarf writes:

Google will be taken to court someday and its cache will go away. Why? Because its clearly a copyright violation when some company makes a copy of my work and profits from that copy. Google is a for-profit company and makes money from advertising. Their cache service is making a copy of my content, without my permission, and serving it to users, again, without my permission. This is completely different than a local cached copy made automatically by your browser for technical reasons, versus a server-based copy made by some third-party company for the enhancement of their services. I’m just surprised it hasn’t gone to court yet.

I have absolutely no idea how to respond to that, and I genuinely like Google as a search engine, but I think he just might be right.