WebPosition Gold and Google- The SAGA:

Penalize you for using web position gold: (April 2003) http://www.webmasterworld.com/forum3/12118.htm
Google and position checking software: (Jan 2003) http://www.webmasterworld.com/forum3/8573.htm
Whats the status of Google vs WPG Users? (July 2002) http://www.webmasterworld.com/forum5/1231.htm
What exactly gets banned using WebPositionGold; (June 2004) http://www.webmasterworld.com/forum5/4799.htm
Web Position Gold & Google IP bans (May 2009) http://www.webmasterworld.com/forum39/3337.htm

By the way, it isn’t just web position gold.  It seems that every rank checking tool out there has been affected by this.  There’s a number of people who think it’s silly for Google to be blocking access to rank checkers.  But I’m pretty sure I know why they are doing it now.  Rank Checkers have a huge impact on “impressions” and skew the search data significantly.  As Google uses this data more and more, they have a strong motivation to make sure their impression data is more accurate for search results.

Now I didn’t realize the extent to how serious Google was about this until I started coding up a tool to do better rank checking and was very confused because code I wrote a few months ago started to break.  I thought Google changed the web page and they changed the web page.  But it wasn’t for everyone.  They changed it ONLY for wget.  Specifically, they removed the rank data from the link just for my wget requests.  EVIL.  I mimiced a real request and sure enough, the rank data came back in.  Pretty crazy stuff.