I'm not sure where to post this as currently there is no a sub forum for Opera Mini yet under apps, so I'm going to post it here for the most coverage (Mods please move this to the relevant section if its not appropriate here):
How to set Bing as your default search browser and get the bing logo in the current Opera Mini beta as there is currently no way to add search engines under "manage search engines" (I have tried various combinations and only this method worked for me):
Disclaimer: once a search engine is removed it cannot be re-added and also you cannot remove Google under "manage search engines"
1) Go to Bing.com
2)Tap on the address bar
3)Click on manage search engines, you will see this screen
4) Delete Wikipedia either via tap & hold or the bin icon
5) Edit ebay either via tap & hold or single tap
6) Edit the entries & save.
7) Press the back key or reload Opera

There you have it, bing is now your default search engine for opera :P.
Edit: According to Legoboyii (link below), you can add a search engine via a long press on the search bar - this was the first thing I tried and did not work for me also on various re installs (hence why you see the attached screenshots have no particular order :P). However I just re-installed again and confirm his method works, but appear to be suffering from stability issues as I cannot load any websites let alone reload bing.com. Furthermore the search engine now defaults to Google.com upon restarting the app. When i posted the guide I tested it via cold boot & soft reset yet the app loaded with Bing as the default search engine.
To compound matters another re-install has resulted in the app now crashing on first start up therefore cannot get past the T & C screen to accept. This is truly a unstable build...
http://forums.windowscentral.com/win...ml#post2757650