@avl: I can say what annoys me there
It's kind of pointless, it's not really helping much besides some very extremely rare cases where you have so much mess in the tabs that they're all over the place.
But it's a bit redundant, there's already a duplicate page highlight feature (which is very nice btw) and page preview which would be enough to tell you what you need.
Also in general I don't have a problem recognising the domain from the favicon, so a non-issue for me.
On top of that the way it highlights the pages when you hover on them there is way too subtle, if it at least did the visuals like the duplicate page thing with a blue underline it'd be better i think.
Basically, it's just an additional clutter that covers your screen with not much value and doesn't seem to be very useful.
Just to note, it's cool you guys keep experimenting and don't just stagnate. I feel like opera has always been pioneers in this kind of stuff, even if it's sometimes a hit or miss.
Also p.s. the page preview is broken, some pages cause complete hang up, i posted about this issue on bugs report long time ago; no response.