I've been trying Opera 9.2 for a week, and I'm pleased with it enough that it's going to continue to be my main browser. The main selling points for me are
- MDI weirdness is mostly hidden now, I hated earlier Opera UIs
- 20-30% less memory use; even after poking about in the guts of about:config to force FF's memory cache to the same 10MB that I gave Opera (which exposes this option right in the UI), Opera consistently uses less memory for the same workload. (Without adding this option to FF, it would max out around 400MB instead of 150MB.)
- feels snappier; opera seems quicker to start rendering something useful on slow-loading sites like 1up.com, although total render time is about the same. It's also instantaneous to open a new tab, which consistently takes around 1s on FF after I've been using it a while. I open and close tabs frequently.
- UI takes up less space: I know it's possible to re-skin FF, but I'd have to google it to find out how. Opera makes it easy. I'm using the Fresh skin for Opera which condenses the File menu and nav bar to about half as much height as FF uses.
- built-in AutoFill, so I save even more space by not needing Google Toolbar
- Download manager goes in another tab by default instead of a separate window. I didn't realize how much FF's behavior annoyed me before.
- Occasional rendering problems, such as when customizing a laptop on hp.com. Blogger.com doesn't redirect to my dashboard when I'm already logged in to my google account.
- Very very slow navigating large pages, such as a slashdot comment thread with 400 comments. Isearch is even slower on large pages and can lock up the UI for minutes if you invoke it injudiciously.
- Sometimes ignores a site's instructions to not cache a dynamic page
- hard to tell which tab is active in the default theme. (Fresh fixes this.)