A tip for 2006, don't forget to check out the new features workshop, and, even if you've used 2004 and 2005, I'd still recommend that you take a few minutes to check out the entries, you might have missed something interesting.
Very Valuable Variables
These are a couple handy System Variables... the following are clipped straight from the help files:
2006 only - Deletes excessive layer filters to improve performance. When a drawing has 100 or more layer filters, and the number of layer filters exceeds the number of layers, LAYERFILTERALERT provides a method for deleting layer filters to improve performance.
0 - Off
1 - When the Layer Manager is opened, deletes all layer filters; no message is displayed
2 - When the Layer Manager is opened, displays a message that states the problem, recommends deleting all filters, and offers a choice: "Do you want to delete all layer filters now?"
3 - When the drawing is opened, displays a message that states the problem and offers to display a dialog box where you can choose which filters to delete
0 Image frames are not displayed and not plotted.
1 Image frames are both displayed and plotted.
2 Image frames are displayed but not plotted.
Suppresses display of the Object Selected Is Not a Polyline ('do you want to turn it into one?' prompt in PEDIT.
Entering y converts the selected object to a polyline. When the prompt is suppressed, the selected object is automatically converted to a polyline.
0 - The prompt is displayed
1 - The prompt is suppressed