if in a wordpress blog i'll hide a link to help the optimization for the site linked, there is some problem? the search engine understand that the link is hide? how i can hide a link? thanks
That's no problem at all - oh except for the 'being de-indexed' thing http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=66353 "Hiding text or links in your content can cause your site to be perceived as untrustworthy since it presents information to search engines differently than to visitors. Text (such as excessive keywords) can be hidden in several ways, including: * Using white text on a white background * Including text behind an image * Using CSS to hide text * Setting the font size to 0 Hidden links are links that are intended to be crawled by Googlebot, but are unreadable to humans because: * The link consists of hidden text (for example, the text color and background color are identical). * CSS has been used to make tiny hyperlinks, as little as one pixel high. * The link is hidden in a small character - for example, a hyphen in the middle of a paragraph. 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"
Its a very common thing, and search engines can understand it quite well. don't do it. however you could do that on sessioned pages though.
google doesn't like hidden text or links so i would not suggest you to do so. there are ways google can tell whether text/links are hidden on a site or not