A rooted phone is a compromised phone.

Trustlook Lab has intercepted a increasing number of malwares and trojans that contain root components which exploit vulnerabilities in Android OS to gain root privilege.
On a rooted phone the apps’ private data can be accessed without restriction (apps like Gmail and Facebook). 3rd party apps could be installed in the background without your knowledge- putting your data and privacy will be in serious danger.
This tool will scan your phone for the root exploit components while detecting whether your phone has already been rooted.

Feel safer now? ;-)