A torrent lens is in the works for Ubuntu 13.10 and Ubuntu 14.04, and it should become available in a couple of days.The Ubuntu dash in Unity, at least for Ubuntu 13.10 (Saucy Salamander), can serve a lot of purposes, and searching for torrents is just one of them.
“I've started modernizing the torrents lens, to make it available for Saucy and up. It's faster and has a togglable nsfw filter,” said David Callé in a Google+ post.
The procedure is quite simple. Users set up the lens and use them by writing “ahoy:” before any query. If everything is good, then you should get a lot of answers.
As the developer explained, an NSFW filter is in place and you shouldn't have any problems. Unfortunately, the development is not ready yet, but the torrent lens should become available soon in the official PPA.
Update: I've been informed that David Callé is not working for Canonical. This doesn't mean that you won't get the Lens, just that it won't get pick up in any official capacity. As the developer has already said, it should be available in the PPA in couple of days.