I've been watching the recent development of the Opera web browser with interest. First they dropped advertising and now they've released a preview of Opera 9, which includes a built-in BitTorrent client.
I've been waiting for this to happen for a while. BitTorrent's a great concept, but it's not the easiest system: building it into the browser could help the idea go mainstream (of course, you still have to go find the torrents).
And although Opera is not as popular as Firefox, partly because it's a closed shop, it is gaining users. Last time out Opera CEO Jon von Tetschner joked that if the program hit 1 million downloads in four days, he'd try and swim from Norway to America (via Iceland) - and although he didn't quite make it, I think he could well expect faster uptake this time.
Note, this "technical preview" is not the final version and the usual caveats for downloading beta software apply.