Recently google announced a new tool Disavow. If have been notified in your webmaster account and worried about unnatural link warning then Disavow can resolve you problem Read that post for more information: http://googlewebmastercentral.blogspot.com/2012/10/a-new-tool-to-disavow-links.html.
As i read about Disavow that it is very helpful tool to remove low quality or spam links from any website but there is something technical and we should describe it deeply that if you upload a wrong file or list of wrong urls you want to remove then it could be harmful for your website ranking position in search engine ranking pages. Therefore every webmaster or SEO expert should be conscious about its usage.
Read the blog post carefully there things are cleared. If you're notified unnatural links in your webmaster account then start removing those link which googles indicates.
I've been sending manual requests... basically using the backlink report strategy - backlinkreport.net/penguin-strategy - documenting my efforts, etc. All those webmasters who don't respond.. the ones that are PR0s or ones with no PR-.. or even the big PR, massive sites with some comment or spam link.. I going to disavow those and show Google the effort I made..
yes of course i agree with you google release new disavow tool removing unnatural links i really likes this my website page rank 5 but not increase last 6 month i check our all my back links and remove unnatural links i hope google next updates my page rank 6 thank you google nice job keep it up