Cool little app that does exactly what it says on the tin. I like using it to find out who owns certain iTunes shared playlists. Often it's as simple as looking up the name of the playlist and then checking their link-local name, since most people don't change it from the default which is their real name. :)

Then proceed to complement these people on their music collections. They will be impressed that you figured it out. Don't tell them you cheated!

Also cool to discover machines running services you had no idea about. Makes for good dinner conversation.

"Hey, I didn't know you ran an SSH server!"
Trust me, I've tried it. Works like a charm.

By host? holy $#@!, that's bad. Like, really bad for the network. It means it's resolving every single service it comes across. There's a reason Bonjour Browser doesn't do that, and it's because that behaviour would be extremely bad for any network of moderate size. If you want an example, imagine Apple's campus network.

Note: this is the author of Bonjour Browser speaking

iStumbler does this and more, and is also free. It allows you to either browse by service (like Bonjour Browser) or by host (like Flame) so you can replace both of those with that one app alone :)