I am running toolbars for: SEO for firefox, SEO Quake, Google Toolbar and StumbleUpon. Lately I have been experiencing alot of CAPTCHA pages in normal searches. Could these toolbars be the reason?
This might be because of your connection... though unlikely, if your IP or connection type is being used by multiply people all searching, the search engine might be implementing this CAPTCHA of a way to be sure it just isn't a robot trying to DDOS one of there servers offline. Maybe check and see if others have the same IP as you and consider running your internet through a proxy. In theory, I see no reason why a toolbar could affect search.
you would have to be doing quite a few searches really quickly to get the captcha. I know a lot of ranking tools will cause google and yahoo to ban you temporarily if you run too many checks during a short period of time.