There are some known issues with searching:
Bing.com has issues with IE8 in a search from an iframe.
Google.com will not allow a search in an iframe
Yahoo.com search may have issues rendering inside an iframe
Dogpile.com does not have any known issues.
The functionality of using a search engine is not explicitly supported by Cisco, but is used as an example of using the Callvariables to pop a screen.