A couple of things about Opera: Press F12 and select "Identify as Opera" from the Quick Preferences menu. Don't want any sites getting the wrong idea now, do we?

Second, if you have your Windows taskbar set to "auto hide" having the Opera taskbar at the default bottom location gets extremely irritating. That put me off Opera (I didn't know you could change it's location at the time, I only found out you could by accident) for ages because I was always causing my Windows taskbar to pop up over the Opera one. Right click a blank spot on the toolbar and select "Top"
Thirdly, go into the Preferences (Alt-P) and under History and Cache, make sure that it always checks for modified documents otherwise you'll have to hard refresh things like forums pages after you make a reply because it'll reload the cached copy instead of download the updated one automatically.
I think thats pretty much it for now...