Again an interesting question from Anil.
Google Search Algorithm = Page Rank + Text Matching Techniques. Page Rank plays vital role in ranking web pages. But it doesn't mean that all pages having high page rank should rank at top. Google introduced and following this pagerank technology and this makes them stand out among other search engines.
Now lets digg deep into the PageRank calculation.
Google's PageRank calculation consists of more than 500 million variables and 2 billion terms. Really hard time for us to predict each n every variable they use for this. But i can list the main things which are taken into consideration and having much influence in the calcualtion formuale.
1) Internal Backlinks
2) External Backlinks
3) Bounce Rate
4) CTR
5) Domain Age
PageRank reflects Google's view of the importance of web pages. Check here for official info
http://www.google.com/corporate/tech.html