@Colin: I actually think 5px is a bit on the thin side. I started with 4px, and it was definitely too thin to have the effect I wanted. I notice that the grabbable border width provided by 2 other currently-popular window systems seems to be closer to 6 or 7px.
I think somewhere between 5px and 7px is probably right for a default 2D theme, but the exact "sweet spot" is probably somewhat dependent on the DPI and size of the user's monitor(s).
@Colin: I actually think 5px is a bit on the thin side. I started with 4px, and it was definitely too thin to have the effect I wanted. I notice that the grabbable border width provided by 2 other currently-popular window systems seems to be closer to 6 or 7px.
I think somewhere between 5px and 7px is probably right for a default 2D theme, but the exact "sweet spot" is probably somewhat dependent on the DPI and size of the user's monitor(s).