i don't like google as the default search engine, it is good but sometimes doesn't do what i need
i used to work with metacrawler until i abandoned firefox
in opera i couldn't find the way to add metacrawler directly until i found the steps required to do it
1. open opera web browser
2. in the address bar write the address of the search page you prefer, in my case i wrote
www.metacrawler.com3. right click on the search box and click on create search

4. in the search engine you can put a name for the new search engine, a keyword and mark use as default search engine to replace google or your current search engine and use as speed dial search engine

just mark what you need and press ok
don't modify the address or the new search engine could not work
if you marked use as default the new search engine should be in use immediately

i tried this process with bing, yahoo, google, ask between others and worked well
hope this info helps other opera users