As I update my four books on AutoCAD 2006, I come across items that surprise me -- features or bugs:
A bug in the preview window of the DimStyle dialog box: change angle units to grads or radians, and then back to decimal. Instead of displaying 60.0000 degrees, it now displays 59.99909 degrees.
The DimArc command has a "hidden" option: Leader appears only when the arc is more than 90 degrees. It draws an arrow pointing from the text to the arc. I don't understand the point to the leader.
Mtext no longer uses <> for default dimension text. Instead, it shows the actual measurement with a blue background. But you can sill use <> with the Text option of dimensioning commands.
While editing dimension text with mtext, you can add [ ] after the default text, and AutoCAD automatically puts in alternate dimension (like metric) after you exit the mtext editor.
(Can you tell I am working on the dimensioning chapter?)