This was mentioned in passing back in 2005 but i though i would re-iterate. I believe by AutoCAD 2005(?) the cookie cutter trim command has been taken out of the express menu and is now command line only. To access the command, type in EXTRIM in the command line. I've had about three people come to me looking for this command over the last month so i thought i would remind everyone where this useful tool is.
For those who have never used the cookie cutter trim (EXTRIM) before, its a great tool to trim out a small part of a large complex drawing or for trimming a hole in a complex drawing. Just make a polyline, rectangle or circle of the area you want to trim around/ in. type EXTRIM and click outside the rectangle to trim everything outside, or click inside the rectangle to trim everything inside. On large complex drawings this is most useful when used in conjunction with a copy with base point. So for instance, your make a rectangle, trim all outside, leaving unconnected lines and such outside the rectangle and then use the copy with base point to copy out the objects left inside the rectangle, make a new drawing and paste to base point. done! sounds like a long process but it takes only a few seconds. Hope this helps,