They don't really care what OS you use as long as you don't ask technical questions. ;D
hehhee, all seriously though, they are good. Besides charging too much for data only service, $ 59.95 plus $ 3 for modem rental for me for Internet only without Cable TV service, the reliability seems to be pretty good.
They also do not block any server ports. I've this site running off of my box with Comcast connection. I also run FTP server and mail server off of this connection as well.
My Gateway box is Debian with DHCPD ( no PPPoE shit ) and I've used with PUMP as well without any problems at all. Except the virus network flooding to my Apache logs, the network is pretty good shape.
They officially do not support Linux ( as well as their comcast.net site is Flash based even for menus : ) but they won't bother you as well ( at least ATTBI unofficially supported Linux ) so it's all good for me.