I like using hot corners to activate Exposé. I also like to use multiple displays to expand my desktop. Unfortunately, when the desktop is spread across two displays at the same resolution, hot corners are active only at the outside corners of the combined desktop, not at the inside corners of each display. You have to take your cursor all the way to the right edge of the rightmost display to activate a right-edge hot corner. And with two wide-screen displays, that's quite a trek.
The trick, then, is just to slightly mis-align the displays in the "Arrangement" tab of the Displays panel in System Preferences. Nudge the display on the left slightly above the display on the right, and two new corners are created: the upper-right corner of the display on the left, and the lower-left corner of the display on the right.
The corners at the far edges of each display are still active, too. So now you have six corners: upper left, upper middle, upper right, and lower left, lower middle, and lower right.
It's not quite the same as having all four corners active on each display, but two short-stop hot corners can save you a little mileage on your mouse.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20041106031749738