This is by far the best gui for making rars out there, even though I'd love to see some improvements :
The preferences don't remember what you entered, so I gotta re-alter the settings each time I'm compressing folders. I think using a separate window instead of preferences might be a better idea (RarMachine does a better job at that).
When compressing a folder that contains an alias (e.g. an alias to the applications folder), it also compresses the items in the folder connected to that alias. I thought the program was slow, but it was in fact compressing approximately 40Gb of items instead of 500mb.
Batch processing (enabling you to drag a lot of folders to the app) would be great too, and maybe a new icon :p ?
Overall though, I think this is a great program, I love the cancel button, the fact that it works well unlike RarMachine, the simplicity, ...