I'm a frequent user of graphic programs. I use PhotoShop and Gimp and several other tools, but one that I'm almost always in-and-out of is Paint.NET. It's become a workhorse for graphics work. Fast and direct, it makes a lot of tasks quicker and easier to knock out. It is arguably a bit light on some heavy-lifting features, even some medium-weight features, but it's still indespensible for many common graphics editing tasks on Windows platforms.
Rick Brewster's blog has some great posts and comments about the forthcoming 3.5 release and what's being carved out for the almost-legendary 4.0 release. I find it a bit funny how different peoples' views are about the early specs for 4.0 clients (system requirements). Some are freaking out but most are accepting it well (like me). I mean, seriously, even if you can't afford a newer machine and you're getting by with something pretty old, you can't get upset at someone for trying to keep their products up to snuff. If they slowed down for every poor knuckle-dragger, imagine how crappy software would be (or crappier in many cases). Paint.NET is a great piece of software and under-appreciated for being FREE in my opinion (although donations are strongly encouraged). I'm eager to get my hands on 3.5 and even more curious about 4.0.