I love, love, love containers. Even when a site I need multiple accounts for has its own multi-account management, containers is better... and most sites don't.
It's perfect for separating out multiple accounts for testing a site during development; it's perfect for separating tabs out by category, each with a color stripe to remind me what they're for. It's basically perfect -- add in a self-destructing private container, maybe, and custom icon support, and I'd say it *was* perfect... but using colors with the simple dot icon is almost as good anyway.
