Yes I have! [webmasterworld.com] (Posted in this forum by me only yesterday). Version 7.50 fixed this particular problem as well as another problem with download extension spoofing (see the changelog for 7.50). A quick check shows that Opera was vulnerable to a cookie path processing vulnerability prior to 7.20 beta, and from memory Opera 6 moved up version increments several times due to security problems.
This is not to criticize Opera specifically. Bakedjake is right about several serious vulnerabilities in Mozilla (and variants), and let's just say that Internet Explorer doesn't have the best reputation either. Overall, Opera has a good security record, and Opera Software appear to take problems seriously and make sure that corrections are made when problems occur. I think that's the best we can ask for. Just don't expect them to be perfect!