Google is a mystery as far as search engine theories go, you essentially have to try and understand what makes one site rank better than another. Although the forementioned algorithms are constantly changing Google themselves have shown link backs play a large roll in a search engines view of any web page, in order to do well a website needs to have links from other sites directly to it. Not only that the websites that link to it are usually respected by search engines themselves. PageRank is google's own measure of a website, there is much speculation on how it is composed but a key factor is proven to be back links, below is a scale that is widely believed to be the backbone of how it judges your website. The amount of PageRank distributed around the internet is believed average at 1 for every website, thats why we begin this at PageRank 2.
PR 2 = 0-6 Link backs
PR 3 = 6-60 Link backs
PR 4 = 60-600 Link backs
PR 5 = 600-6000 Link backs
PR 6 = 6000-60000 Link backs
PR 7 = 60000-600000 Link backs
PR 8 = 600000-6000000 Link backs
PR 9 = 6000000-60000000 Link backs
PR 10 = 60000000-600000000 Link backs
We used a base number of 6 for this example although it is disputed whether it could be 5 or lower. The amount of back links your website recieves plays a large role within your search engine positioning but a strong anchor text and title tag for your links is also key to success, you can see how to do this as demonstrated below.
a href="http://www.linkhere" title="Keyword Title Text" Keyword Anchor Text
PageRank analyses more than link backs. External links are known to "leak" page rank from your website, in simple terms - your website can cast one vote against each websites it links to, if these are external links it takes from a pool of PageRank that your website has to offer. It is recommended you either seek recipirocal links from websites you link to or use other methods like javascript to prevent your PageRank from being dispersed from your website.
Digg
del.icio.us
FURL
Reddit
Yahoo!
Favorites