I normally have around 10 different applications open and running at any given time – a persistent set of communications apps (Adium, Mail.app, SpamSieve), a couple browsers (Safari, Camino), and the 2-4 apps necessary for whatever I’m doing at the time.
Adium’s Preferences really let you dial it’s presence down.
In Advanced > Contact List > Window Handling select Automatically hide the contact list > While Adium is in the background.
This effectively hides Adium when it’s not the active application, like when you’re not sending messages.
Unlike Mail.app, Adium let’s you turn off the unread message icon in the Dock
Preferences > Advanced > Messages and uncheck Display a message count badge.
In Camino, I’ve turned off Flash animations – so much less annoying when they’re a click away. Preferences > Web Features and check Block Flash animations
Lastly, I played with Growl for half a day, while its purpose is to provide a single channel for all notifications, it was too much and felt like I was on a Windows box. If my job was to watch Growl all day, it’d be perfect. But that’s not my job.