yeah fire is one of the best "simple" apps for mac os x out there. and even better if you have accounts with different messengers. the only downside, is that sometimes i get problems with icq's server, but aol and msn are really good.
after you learn how to customize it, it will surprise you, and since it lets u create your own groups with people from different messengers, it makes it even better and simpler to use. the las version 30b? or something like that, its way overdue, i think it needs an update, but it still good. the other app that consider to be great is sputnix, for audiogalaxy satellite