I've been using Opera 10 since the alpha was released, and I can rarely stomach opening up Firefox anymore, although I need to for firebug. Firefox just seems so... bloated. But I digress.
I don't use Widgets, but I do use the BitTorrent client quite a bit. It's a lot more straight forward for smaller downloads than opening up uTorrent. For larger downloads, I do use a dedicated Torrent client, however.
Edit: Even diehard Opera fans have to admit there are a lot of cool features barely anyone uses. Opera Widgets? Opera's BitTorrent client?