It's interesting how that one experience completely changed your perception of Opera even now. Definitely applicable to startup life - don't take the easy monetization, it may come back to haunt you.
To be clear, I have no opinion about Opera now. My negative opinion expired a long time ago. Opera is merely one of the "browsers I don't use" in the same category as Konqueror, Safari, and Epiphany.
What it did was lose me at the only point it ever mattered for a product with a long life. Firefox has satisfied my needs since, and I've never had the will to evaluate Opera again.