I really like Aperture the more I use it, being a Gov't employee, I get a nice little discount as well, so that helps, as it's pretty expensive, but honestly, it's got most things I need, and I only find myself needing to venture out of it for very few things.
Pixelmator can be found
here, it's a Core-Image based editor. Core Image is built into the OS, so it's lightning fast. Don't know if you've ever used a lot of filters or whatnot on Corel, but they get slow, slow, slow at times. Most stuff happens realtime in Pixelmator, so no applying an effect, waiting, then having to undo if you don't like it. It also reads a bunch of filetypes, so there is a good chance your old stuff is readable.
The negatives are that it's 1.0 software, and as such, it's going to have growing pains. It's not as full featured as Photoshop, but it's also $60, not $600. The interface is a negative for some, I think it's beautiful, personally, it's pretty much what grabbed my attention, but I understand some of the negative comments it's garnered. Some relatively common tools of other popular image editors are missing as well, but that's part of it being so new. I suppose you have to release it at some point, with or without everything you wanted to cram into it, which leaves some people wanting more.
I'm personally a hobby guy, I don't need the full power of Photoshop, and at the time Photoshop Elements wasn't available for 10.5, so I got this, and I'm pretty happy with it. I did my avatar with it, and up until I got Aperture, all the fine-tuning of the photos I was doing.
One thing about iPhoto/Aperture, they seem to work together, which is nice, you can view one from the other. I got rid of the iPhoto library, I like Aperture better, but you can choose to leave your photos in iPhoto, and just reference them in Aperture, and vice versa if you like the simplicity of managing them in iPhoto, and the extra features of Aperture for editing, they both also allow you to select an external program to do extensive edits in.
