The more thought I've put into it the more hurdles I find the would make it difficult to come up with pure data to determine searcher intent from this side of the search engine.
I've come to the same conclusion. It takes an immense data-mining effort to do this, with a lot more data than one - or a hundred or even many thousand websites can accumulate.
One rough breakdown of user intent is informational, navigational, transactional, with the question of local intention (or not) folded in to various degrees. Google's been at work on this project for many years and they still don't get it right all the time. I also think that Google's breakdown is much more granular (and possibly personalized) than this top level taxonomy.
One interesting facet of Google's work with user intent is that it also requires automated taxonomies to be created for various web pages and websites. So Google's job requires classifying the various queries, classifying the websites, and then matching them. In many cases, queries also seem to need a mixed set of results, at least for now.
The only practical steps I have been able to come up with are in the keyword research I do for a website. Before I even think about targeting a new keyword, I always check the Google results (including the suggestions!) to get a feeling for how that phrase and its relatives are currently classified.
If Google sees it as having one intent but the website is of a different nature, then that keyword phrase may be a lost cause for a given website. And the real kicker can come if Google re-classifies either a site or the query phrase itself. A healthy frow of search traffic can all but dry up overnight ;(
