[Martin]

For some reason we don't allow search engines on our forum. We do have it in our joomla and would like to implement it also in the smf.

My question:

google does get information about content and we do block unwanted ad-sites. Would it run accurately within smf even w/o letting google examine the forum?

If we had to allow google: is there a way to tell the bot not to cache the content but just examine it for the ad?

On paper, the answer is that you can use robots.txt to diallow Googlebot while allowing the Adsense bot.
http://www.google.com/support/webmas...366&topic=8846

However,

There's recently been a change where all the various google bots feed a common cache, to reduce the need for multiple spiderings of the same page. So it really depends on your goal for keeping out the bots. If all you want to do is stop caching, there's a meta tag for that.

see also
http://www.mattcutts.com/blog/crawl-caching-proxy/
http://www.mattcutts.com/blog/bot-ob...ing-googlebot/