I've considered the proxy approach. Consider that proxies do not see the content of SSL connections though. Which may be just what you want, or absolutely not what you want, depending.

The archiving he outlines is reasonably cross platform - most platforms have ports of the tools in question, and you "just" need a way to get the browsing history.

The trickier part is good/proper indexing if you want to be able to do more than look it up by url.