I used hiding text only for google ad placement purpose. Is this harm to my site. http://www.geethasagare.blogspot.com Thanx
Yes. It worked back in the nineties, but you'll be penalized for it today. Anytime you try to "trick" or "game" the searchengines you'll probably get penalized. Even if the searchengines don't catch it some competitor will probably report you and they'll do a manual review.
They explicitly say you can be de-indexed because of it "If your site is perceived to contain hidden text and links that are deceptive in intent, your site may be removed from the Google index, and will not appear in search results pages" http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=66353
Yes, It do harm, As it is the black hat method. Google hates it, So, you will not get more traffic from google or other search engines.
It's not just harmful it's very harmful ... your website can get penalized .. stop using black hat seo techniques won't work in the long run.