I regularly have more than 100 tabs on my tab bar in Opera 12. This seems to happen because I've been using the tab bar both as a way to keep open tabs related to what I'm currently working on, what I will be working on soon, and also pages that I want to read or check up on later. I can often find my way back to what I want simply by its approximate position on the tab bar, of I use the Windows panel to filter my tabs.
This has been possible because Presto is an efficient little engine that handles these kinds of situations better than anything else.
In Opera 15, though, I have found that opening a lot of tabs makes for a rather poor browsing experience. As a result, I have started adding pages to my Stash whenever there's something I'm not going to do right away or in the immediate future. This seems to work fairly well, and a major advantage of getting tabs out of the way is that my tab bar stays readable and (more) usable. Stash also lets me filter items, just like the Windows panel did.
This feature will only get better as it improves over time as well.