Now in terms of addons, I would probably say that I am a medium user, falling somewhere between Paradise and Veloreynn. I probably have the standard addons that most have including Grid, Atlas Loot, DBM, and Omen. One nice addon that I've had for a while that I really really love is WIM, WOW Instant Messenger.
WIM basically turns your whispers into their own individual chat bubbles. I love it for several reasons. I can step away from the computer and come back and not miss any whispers. I don't have to scroll up to see if anyone whispered me anything. Their last whisper to you is just in that chat bubble.
Secondly, it solves the pesky issue that I'm sure all of us have had where we whisper something to the wrong person. WIM has definitely reduced my need to say "Oops, MT". I think the last time I remember doing this was when I was poking fun at one of Jess' lectures. The whisper was intended for Vel, but I accidently sent it to Jess. It wasn't too bad because Vel and I both openly poke fun at Jess in both raid chat and over vent, but this MT could have been bad!
Finally, you can set WIM to record a history of your whispers. It's kind of a nice feature to have in case you ever have to use whisper history to bribe anyone (which I would of course never ever do).
The only amusing part of using WIM is when you have a ton of whispers going on at the same time. As Jess and Kalthan remember, I logged on one night last week into Ironforge and stood there for nearly an hour with 7 or 8 chat bubbles open and going on at the same time. They took up my entire screen so that I couldn't see anything beyond them!