Shoutbox

I like the tag completion idea, i like a lot of the other ideas so i won't list them all.
Script script script!  A layout like in mIRC would be good, with sections for code for aliases, tags, menu items and events.
Disabling the blue 'toast' popups when you're busy
More popup options for when you're online, particularly when a status changes from busy to online etc.
And if you're going to make more easter eggs (please do), please don't make them as useful/fun as the sounds!  I don't think i could stand another wave of newbies asking for them.

And if you don't add all the features I want, provided you do add scripting we can make them all ourselves