Opera released the beta of its Opera 11 browser with a nice feature for those of us that are heavy on the tabs: Stacking.
In a nutshell, tab stacking allows you to group tabs by category (see Opera blog post). When you hover over a tab you can see more options. If you frequently have 15 to 20 tabs open this feature could be quite handy.
This storing of tabs looks like this:
Opera's feature is something that's likely to be integrated into other tabbed browsers. The big question is whether tabbed browsing will entice you to give Opera's latest browser a spin.