An update to Growl will make notifications start playing nice with Mountain Lion.
Growl version 2.0 is now integrated with the ML Notification Center. Up until now, it's been a huge pain in the ass to use Growl with the latest version of OS X—notification and Growl banner alerts would show up in the same spot by default. So you'd either have to ditch Growl, move the location of its notifications, only use apps that support Growl, or use some kind of third party hack. But now life with ML is a little better. [Growl via Cult of Mac]