After xmms-mad-0.5.6-r1 is emerged xmms hangs or uses 100% cpu on pre-buffering or after playing back the buffered part of a stream. Basically xmms-mad breaks stream playback capability of xmms. Simply unmerging it solves the issue. Maybe resolve by explicitely masking it in portage?
mp3 streaming isn't supported by mad plugin yet. use the mpg123 input plugin if that's what you want to do (just disable mad and enable mpg123 int he plugins preferences). You can bug them upstream, but I don't think it will help much ;)
*** Bug 105421 has been marked as a duplicate of this bug. ***
*** Bug 102309 has been marked as a duplicate of this bug. ***
Not sure if this is helpfull but I see the following message fill up whenever I try to use xmms to play any streaming urls. ** WARNING **:: ctrl_write_packet (): Failed to send data: Bad file descriptor The console is full of this messages till i stop xmms from connectiong to the streaming url.