Some web sites just don’t load with Opera, while they properly load with any other browser.
The reason is that when there’s both an IPv6 and an IPv4 address for a host name, Opera tries the IPv6 address first and miserably fails if it can’t be reached even if the IPv4 address is fine. Does it assert that everyone on the planet can reach IPv6 addresses?
This is with Opera 9.5 and MacOSX. Maybe other versions/platforms work. But in the meantime, Opera is not a browser I’d recommend to any non-geeky guy.