If 10% of the world's Internet users are on Opera, where are they?
That's not counting those Opera users who switched their User-Agent string to MSIE or similar because of stupid JS detection like MySpace's.
That said, our own traffic shows 0.80% Opera users, which puts it just above RockMelt. It's silly to actively filter them out as MySpace is doing here, but would be equally as silly (for us at least) to devote any resources to dealing with any Opera-specific issues, until the usage stats justify it.
So if you run US-focused site, there isn't really reason to care about Opera, and test for it. Blocking it (or any other browser) is bad though.
The "historical reasons": Opera was by any means the best (serious) browser out there, but it was paid. People in these countries weren't paying for software anyway, because their income was well bellow western standards while prices were same, and as a bonus, there was no one who would care. So while someone on the west would rather use something free (like IE), people in (for example) Ukraine picked the best. That's why first decent browser (Firefox) took over the west so fast.
Looking at hits is doing it wrong - profit is where it's at, what proportion of profits come from Opera users.
[For example, hypothetically, they might be highly paid trend setters and amount for a disproportionately large profit share on a fashion site or such.]
I'd rather see a number of users who have set it as their default browser.
From: http://www.opera.com/press/faq/
"How many people are using Opera? Today, more than 275 million people are using Opera every month."