While I can play indeed an AAC-stream, the load is too high: mplayer uses 50% according to top, so when I want to to something else while playing the stream, the sound stutters. But that seems to be a problem with mplayer, because the load is equally high while executing "mplayer http://somafm.com/groovesalad48.pls" in xterm.
The same stream playing with the Nokia mediaplayer adds nearly no additional load. (btw. mplayer-1.0rc1-maemo.23.n800)