http://www.linuxmint.com/blog/?p=142
It explains why Mint's google is the way it is and how you can revert to the default google.
Excerpt:
Just think how good Mint would be with full time employeesThe reason we changed from default google to a custom engine is because it generates a lot of revenue and this single plugin could potentially make Linux Mint into a company which actually hires full-time employees.