I downloaded a Pixelmator demo and do agree that it's a brilliant program. $30 seems well worth it.
In defense of GIMP, the program looks better on Debian Linux, where it is a native application on Linux. It is usable, and has many wonderful plug-ins and scripts that others have created and shared. In defense of open-source in general, it serves a purpose that there is no excuse for piracy or warez because no one can say they have no choice. But there is a line between finding usability with open-source and being completely freetarded in one's determination to pay nothing. Which is why, even though I'm well adept at Linux, there are reasons to pay for a commercial OS and commercial apps.
Seashore with a few Gimp plugins would be very nice. But it's not there. Right now it's basically something like what Irfanview is for the PC.