Does anyone here use Paint.Net as their primary design program? Or at least use it as a secondary design program? How long have you been using it? What is your main reason for gravitating toward PDN and away from Photoshop? What are some of your must-have plugins? 

Paint.Net is my main design program. I've been using it for over a decade and have been extremely happy with it. My main reason for using it is because it's completely FREE. I use a ton of plugins, effects, etc. so I'll just list my top three that I use often - Drop Shadow, AA Assistant, Glow.

If you haven't use PDN yet, you have to at least test it out! You may find that you like it and can stick with an older version of Photoshop and just stay up to date with PDN.