And there's the fact that its rendering of 1px vector rectangle borders depends on their location. Yup, sometimes they render a little bit thicker[1], which can be fixed by moving it up or down a couple pixels. I kind of hate Photoshop, except it's actually 10x better than anything else at what it does[2]. RIP Fireworks though.

(As of CS 5.5)

1. Photoshop does antialiasing/subpixel rendering on vector shapes, so while "a little bit thicker" is of course 2px, the second row of pixels is blended with what's nearby.

2. Haven't tried GIMP for a couple years though. Also I've switched to Krita for digital painting lately, and actually like it more than PS.