One of the problems that has plagued AutoCAD 2008 and it's verticals has been the bloated scale list. Scale list entries are propagated from drawing to drawing similar to the way named layer filters did back in AutoCAD 2002.
You may not even be aware that this problem exists in some of your drawings. To take a peek, click on the Annotation Scale popup located in the AutoCAD status bar. If you get something that looks like the image below, it's time to clean up.
If you program with autolisp, you have probably used the command function at some point, probably to construct drawing entities. There is certainly nothing wrong with that. However, if you are working on a large program that constructs a lot of drawing entities, you may have noticed that the command function runs pretty slow.
I put together some tests to compare the (command) function to two other methods of entity creation, (entmake) and (vla-add...). The test constructs 1,999 line entities using various methods.
Starting in AutoCAD 2006, you can specify a highlight color and opacity to your selection areas as illustrated by the green area shown in the example below.
Below is a description of these options and how to change them.
If you want to go through the OPTIONS dialog, open it up and switch to the Selection tab. Click on the Visual Effect Settings button. Everything you need to control is there on the right half of this dialog, shown above.
Read more about Selection highlighting in AutoCAD
In AutoCAD, you can assign a non-continuous linetype to a 3D polyline, but it will not display or plot.
If you need 3D polylines, and you need a non-continuous linetype, for example to represent the flowline of a ditch - there are a couple of workarounds. Both assume that you have assigned the correct linetype to your 3D polylines.
Here is a quick guide on setting up a layout (or paper space) for plotting in AutoCAD 2000 and later. I used AutoCAD 2008 for these steps, and most of these steps should apply (except for the viewport locking) in all versions, 2000 and later. I know this looks like a lot of steps, but it's really easy. The best part is once you set up a layout, you never have to do it again. You can import this layout (or any other) into any other drawing.
Read more about Layout (paper space) tutorial: Part 1