limewire(and bearshare too) has a quality bar with every result.
bearshare(and phex) show the type of server running on the other host.

can someone tell me how they do that?

(i've written a simple client and read the spec, but couldn't find an answer.)

Try posting on http://bearshare.net/ someone there can probably answer that.

most servents sent there name with the http header when a download is requested. thats probably the way to find it out.

but i've no idea how the quality works...