But even if it is useable, the question is whether it is good in the sense that Todd said. A glance at [link|http://secunia.com/search/?search=Opera|http://secunia.com/search/?search=Opera] tells me it is not. Just glancing at the last 2 months of reports, I see 5 security vulnerabilities, 3 of which could wind up executing arbitrary code on the user system. (One is entirely Opera's fault, one is due to an OS/Opera interaction, one Flash/Opera.)
That makes it not good in my books. And the ungoodness would be obvious if a competitor set out, as Microsoft did, and deliberately tried to find the weak spots and make sure that lots of websites tickle them.