From the horse's mouth:
Google's Terms of Service do not allow the sending of automated queries of any sort to our system without express permission in advance from Google. Sending automated queries absorbs resources and includes using any software (such as WebPosition Gold™) to send automated queries to Google to determine how a website or webpage ranks in Google search results for various queries.
Ranking reports are no longer accurate in any case since Google uses "behavioral search". For instance, anyone signing up for a google account (gmail) authorizes Google to track their ip address and past search history in order to better "customize" their search results. That means if you and I were both signed into our google account and performed a search on the same keywords we could receive totally different results.
Also, now it is very common to be on page 1 one day, page 3 the next day, and back on page 1 the next day. If you only look at your rankings it can paint a very grim picture, when in reality your traffic could actually be going up. Good traffic is what counts.
You'd be better off pouring your valuable time into looking at your host logs & installing Google analytics.