Tipster Leif Pedersen sent this tip for using the AutoCAD Fillet command to extend and trim linework.
"I often use the fillet function as a combined extend-and-trim function. Just set R=0 and it will extend and trim lines together."
Notes from Cadalyst tip reviewer Brian Benton: You may know this tip already, but it is worth your attention. Setting the Fillet or the Chamfer commands to 0 radius (or 0 chamfer) will extend and/or trim the selected objects to their intersection points. If they are polylines it will also combine them into one polyline. Another way to execute this trick (in more recent versions of AutoCAD) is to hold down the Shift key while selecting the two lines to fillet, and AutoCAD will default to a radius of 0.