Is it true that Google offers Web History Data to premium AdWords customers to improve their campaigns (e.g. indirect AdWords)? I heard it from different [trustful!] sources.

yes they do, but that's no secret. so no trustful sources needed ;-)

but google scares me – they have too much info

Well, it'd be anonymous like...

anonymous or not – i dislike the way google hides active web history tracking from hte user. no transparency at all