In 2011 what is the most key factor for getting high rank on Google?

As at the beginning on-page and off-page SEO.

Good content
low bounce rate (a high bounce rate can kill your keyword)

link popularity will always be the main key for ranking a website. Its not the quantity but the quality of backlinks will determine the search engine ranking. Back links should be from differet sites with differed domain exentions like .org .info .biz and many other not just .com
Slow Backlink building will determine higher ranking . Search engine will try to know that your back links are made by humans not by automatic program.
there are many more factors.

With the new Panda update being incorporated, the content of your website forms the foundation for your SEO functions. So I would advice if you really want your page to be ranked higher up in the search results then take pain in writing content relevant to the purpose of the website. Once your content is up to the mark then link building can be done.

Ok Mr Imagine work, but I listen that Panda is only updated till now don't followed by search engine.

What? I don't think I got you completely. Panda is new the new search algorithm being followed for Google search results. And it very much has been incorporated into the Google search results. Haven't you read so many websites being axed because of the Panda update. Content based websites are the one particularly being hit.

Links and sharing on social media both are key factor of ranking.