I have now used DVDAS for a couple of projects, and I find that I am quite pleasantly surprised and pleased with it. Although I find some things not fully intuitive (i.e. I would have designed them differently ) overall it is very comfortable to use.
I especially like the features that give me more control and flexibility, such as control of key actions (suppressing the Menu key during my standard pre-menu intro) and being able to add more complex menu structures, such as adding an "Info" button to the main menu which explains the origins of the DVD and when it was produced.
It has worked 100% with no issues or problems, and it seems quite fast.
The only drawback in my workflow is setting of Chapter/Scene markers. When I was assembling my DVD in PRE, I would just have to tab to the next scene and hit the Add Scene Marker button. Now I have to manually search through the video and manually place them. On the other hand, since I am importing MPEG into DVDAS this is probably a good thing as I can shift the marker to be in an i-frame (orange instead of yellow) rather than take the program's selection.
The only thing I am concerned about for the future is that a version will be available when I am ready to start producing Blu-Ray. I guess we'll just have to wait and see. I understand that the Pro version (sells only with Vegas) does have that support.
Anyhow, highly recommended - and don't forget Steve's book!