One major shortcoming of OS X's Finder is how poorly the contents of Finder windows are updated. Often an inactive window will show information that does not properly reflect the true contents of the directory until the user clicks on the window. At best this is an annoyance, and at worst this can lead to data loss by, e.g., selecting the wrong files for some action such as (oops) deletion. I have written a simple AppleScript, called "Finder Refresher" that will correct this problem. It seems to work well, refreshing all windows, even when the Finder is not the front application, and taking very limited processor cycles.
Mac OS X 10.2 or later