A few day ago I was speaking to a friend who was testing out SliQ Submitter for me and providing some useful, constructive feedback. He was wondering what tools I used to check the ranking of my site on Google for different keywords. I don't use anything other than Google searches by hand but I thought I'd look to see if there was anything on the market.
I soon found a tool called WebPosition Gold or WPG for short. This tool allows you to automatically track the performance of sites on Google and show nice graphs of the historical trend. Trouble is that with a bit more reading online, it turns out that Google mentions that use of WPG is against Google's terms of service. the terms specifically name WPG as well as saying that similar tools are also not to be used.
To use WPG you have to a Google API key for their SOAP search API. Google no longer issue such keys and there are stories online saying that WPG users are now finding that WPG gets blocked. The future doesn't look good for WPG.
When I think about, it seems fairly clear that tracking a few keywords is interesting but not necessarily informative anyway. What really matters is traffic to your site and conversion of visitors to sales. You could be performing really well for certain keywords - and improving in performance too - but really you need to measure traffic. Google itself provides a better measurement tool - Google Analytics. If you have the time, Google Analytics can provide valuable data about the performance of your website - traffic figures, how people got to your site (not just SE performance) and where they went went they landed on your site.