Streaming Servers

I know that this is not the primary focus here, but does anyone have any good data on icecast or shoutcast streaming server requirements (or a pointer to such data)?

If you've got any info on what you're burning relative to the number of simultaneous users, that would be helpful. Bandwidth is easy to estimate, but specifically, I'm trying to quantify the kind of CPU and memory requirements needed per feed for a reasonable quality stream, even if it's a ballpark (and some info on your server setup).

Thanks,

Roger