As far as I'm aware, wordtracker show searches from the last 90 days. If people search for keywords in their address bar (I assume that's what you meant?), then they're usually redirected either by or to a search provider of some sort, so this is much harder data to obtain reliably.
Whether or not it's accurate (and you should use it or not) depends on what you use it for. I would factor it in with a reliable source like website statistics and any other sources you have. You'll likely find that the more popular the keyword, the more reliable the third party source.
