Sadly, Mango doesn't add anything to the notification system. This kinda bummed me out since it's probably my biggest complaint about the OS. But there's too much I love about it to switch over that. I've learned to keep the tiles for all of my apps that give notifications in the same place so I can take a quick glance at all of them when I need to.
Currently, the OS doesn't support background audio for third party apps. I'm hoping that's why Pandora isn't available yet. Mango is adding background audio so keep your fingers crossed about Pandora
In the mean time, there's always Slacker and Last.fm.