Why?
As you can see here: http://ubuntuforums.org/showthread.php?t=367494 People would be very into the idea... If by some chance you live under a boulder and don't know what libnotify is, it is our fancy no notification system, which uses the system theme for showing alerts, there is a plugin, cleverly named Gaim-libnotify, which uses libnotify for gaim alerts, such as online/offline, new messages, etc. Many users have this little plugin for gaim, and without really knowing who logs on or off, and such... there isn't a lot of point to having an IM client. This would make the default desktop seem that more professional, and it would be a step away from the oldhat guifications, which was great in its day, but looks out of place now, when we have something you don't even need to theme, it just does it to look great with your desktop.
How Could it be done?
SUPER EASY! It could be approached one of several ways, you could make the gaim-libnotify package a dependency of ubuntu-desktop, as so you could have gaime even if a user decided to uninstall this plugin, you could create a metapackage for plugins which installs all the functioning plugins to gaim (this method would mean we shouldn't set any plugins on out of the box though as this might be installed manually.. so this isn't... the best way to go, I suppose). Again, it could be a direct dependancy of gaim..but what if they want to (for some unknown reason) remove this plugin, but not gaim? I say it's most Ubuntu-like to make -desktop demand it.
Why can't they just install it themselves?
Simple... most people haven't heard of it! It seems like everyone knows of guifications, most people don't like it for the sake of it not meshing with the system. Installing it by default would mean the users who may never hear of it see a more professional, and polished looking gaim. We all know despite what people want it to be, the new "I'll just try it out for a minute" users want flash, not face-melting flash, but enough to say "WoWo".
Looking forward
Again, it would simply make the default desktop look more refined, there is not one "typical user" who wont have at least one one account with some IM service, and they are used to seeing alerts when people Sing on/off, it's as simple as that. If making it more at home for the new user isn't your bag, do it for the pure sake of making things flow, and make them more efficient.
Discussion
I like this idea a lot. It integrates much better than guifications and it doesn't have the annoying guifications defaults. (by GuidoLoupias)
Warbo: Packages can have different levels of dependency, namely "depends", "recommends" and "suggests". I think recommended packages get installed automatically by default along with dependencies, but suggested don't. If it isn't already, Gaimlibnotify could be recommended by GAIM and put into main, then it could be installed by default (and wouldn't have all of that messy removing of ubuntu-desktop for trivial things, even though it is needed for upgrades).
MikeBasinger: Does this behavior look to be the same in Pidgin 2.0, since it will probably replace Gaim before the Gutsy release.
(Spec writers note: I'm pretty sure that won't be a problem with the next release, they're making the meta package thing less of an issue anyway, but I get what you're saying -BryanHaskins)