Opera have about a 2% market share so I'm tempted to leave it - the big three (IE, Firefox and Chrome) seem to run it just fine...
A far as i've read, the 2% claim is American slant. Opera is the only non-American browser in your list. I heard that it has about %15 in some European countries, and as much as 20% in Russia.
For myself, having enjoyed supporting Opera for many years, i have finally switched to FF nightly build. Main reason is Opera doesn't yet support things like Drag & Drop, and have also fallen well behind on other HTML5/CSS3 support. Also C2 content was hard to test because Opera uses the arrow keys for scrolling the browser. But the final last straw was actually speed comparison.
Btw, here's an interesting quote:
"IE supports DnD from IE5 but it doesn't support File API even in IE9.
Opera supports File API from 11.1 but doesn't support DnD."