Hello SEO guys,
How footer links affect site’s ranking in Google? For ex, ther’re a lot of links with anchor
text “Powered by” and url to my website.
Oh yes footer link does have affects on your site. Suppose if you are a web designer then footer is used to acknowledge the creator of the page/templates or the person/webmaster(would be you). Sometimes footer links are used to have additional acknowledgment links for site and use as a backlink in return to the free products or services which you would definitely want for your site. 
[FONT=Verdana]Please search the forums before posting a new question. This one has been asked a number of times already and there is a recent active thread on the subject here: http://www.sitepoint.com/forums/showthread.php?966074-Are-page-links-in-footer-good-for-SEO
Please join in with that discussion. Other relevant threads include http://www.sitepoint.com/forums/showthread.php?871897-Web-Designer-link-in-footer-of-client-s-site and http://www.sitepoint.com/forums/showthread.php?888305-losing-rank-because-of-footer-links [/FONT]