One of the things I find myself doing all the time is making columns wider in Open and Save dialogs. I have a bunch of file names that are really long (the downloadable names of my presentations), and I find myself grabbing the little handle at the bottom of the column a lot to widen the column. Last month's MacWorld to the rescue. You can double-click on the little abraded area at the bottom of the column and it will resize the column to accommodate the longest file name.
Going one step further, you can right-click on the abraded area and get a pop-up menu that lets you choose one of three options: Right Size This Column, Right Size All Columns Individually, and Right Size All Columns Equally, as shown here:
Try as I might, I couldn't get a keyboard shortcut to stick for this (normal keyboard shortcuts don't seem to work in Open and Save dialogs). If anyone can, I'll be grateful. But this is good enough: rather than resizing by hand with the mouse, I can let if figure out the correct size (alas, still with the mouse).