Opera Mobile has been randomly closing down on my N8. I've noticed others reporting the same issue. It is a compatibility issue with the Nokia keyboard. Change the keyboard to the Opera one and it should work OK.
Hope this saves others some time!
Opera Mobile Problems
I've found that just turning off predictive text fixes this problem for me.
Unfortunately that's the main use for the original keyboard!
The new opera mini beta does allow predictive text though, so give that a try.