I've used Opera for a long time, and when I started using it it was simply alone on top of a lot of crap browsers. Now there are several decent alternatives, all of which are very frustrating for me. I work on multiple computers and have multiple computers at home. I'm lazy. Hence, no plugins should be required, so I get the experience I want installing just the browser.

For the most part Chrome or Fox or even IE10 behave similarly enough that I can almost use them instead of Opera. I think there's just 2 exceptions. Whenever I use another browser I find myself getting frustrated with 2 things: (1) Nothing happens when I "roll-left" over the mouse buttons (navigate back). (2) Tabs MORONICALLY cycle left-to-right, rather than in most recently used order. Both are show-stoppers for me, and I don't care if a plug-in can fix it, as long as Opera is otherwise more or less on par with the alternatives.