The custom control I've been working on required drawing custom shapes on each side of the control. The shapes needed to be the same size and I was sure that one was a couple of pixels shorter than the other, but it was difficult to tell with the naked eye. I was wishing that the WinForms editor in VS 2008 had something like Photoshop's Guides: horizontal and vertical lines that can be placed over the image to aid alignment.
Since the real issue was to create an edge that I could use to judge the length of my graphics, I pulled a panel on to the form and stretched it across the control. That worked okay, but the panel was still 8 pixels high and I often had to move it when I resized my form or control. The former was solved easily enough by setting the height of the panel to 1 in the Properties window, but now it was very difficult to get a grip on when I needed to move it. Then it occurred to me that if I anchored the panel to the sides it would stretch as the form stretched. Shazam! Instant guidelines.
At some point I'll write a macro to do this automagically, but this is good enough for now.
If you find this useful, let me know.