Google Analytics is a tracing tool provided by google for free.
We can use it for our site to trace. many web companies give offer to trace our site.
but that tools are not free.we have to pay.google updated Google analytics recently.
This tool offers more informations like.

• who are visitors to your site.
• which keyword they are using to come to your site.
• How many pages are visit.which browser and OS they are using.
• daily,weekly,monthly  views.
• which country people see your site.
• Reference sites.
• set goals to our site.
• Which pages people like and which pages people does not like.
• In page Analytics that means people like hyperlink in yoursite by pages.                                                            

For more info see ..http://en.wikipedia.org/wiki/Google_Analytics