I'm a Skype/Growl user, and I like the way Growl notifies me while Im' working in other programs when a new message has arrived. Just one thought: The alert does not support emoticons or so it seems. It never replaces (y) for example. Would it be possible to support some basic set of most used emoticons, so those would show up?
It's a bit stretching it probably, but it would be a "nice to have"
As far as i know, right now the only things a growl notification can display is an icon (such as the growl claw or Adium duck), a title and a string of text. This would need to be supported by growl itself, and i think i remember one of the devs saying this is not being planned.