Minimum Selection Size
This is just a small thing I noticed but it seems like it would be nice. I was wondering, have you considered setting a minimum size for the selection? Right now when you use the selection tool you can actually make the width and/or height zero, so it's just a thin line and it doesn't select anything.
It would be nice if the minimum width/height was one so you could select thin lines of pixels easier. It's not really a major issue but I just happened to notice it in a few other programs that did it and thought I'd mention it.