I know of a few forums that only allow spiders to crawl their archives and no other pages of their site and I tell you what, they rank very well in the search engines.

As we all know the archives are very clean and usually are more content relevant throughout than the regular pages of your forum.

So it brings up a question, should you just use your archives for SE purposes?

I personally like it, to serve spiders the archive, with the real forum urls. So that a user from a search engine, directly views the forums, instead of the ugly archive.

Well, spiders used to be bad at crawling dynamic pages (ie ?file=blabla), so that's when the archives came in handy. I'm not sure whether or not this is still the case though.

Archives can make a lot of $$$ if you have enough PR to toss to them.

PR? Public relations? Could you please eloborate?

Google Page Rank. If you can get your main archive to a PR 5, google will crawl most if not all your archive threads. I have 1.2 million pages in google. Most never see any traffic, but a few rank rather well.

I've never quite understood the PR idea.. so I gave up :p

My archive actually gets a ton of activity from the spiders, more links to the archive = more spiders.