Hi,
when I just did a few full-screen captures (pressed F11 in Internet Explorer to capture all of the visible area, I didn't need what's below), I found out that SC always captured the screen in 1282 x 1026 instead of my 1280 x 1024 screen resolution. Looks like SC added a white one-pixel border to every side of the capture.
I also found out that my SC installation wasn't the latest version, but updating it to the v2.37.03 didn't change this.
I also checked the options (which by the way are called "Preferences" in the tray icon menu, and "Options" in the options window that pops up), but the "On Capture/Add Border to Image" option isn't enabled.