New checkbox on latest drop of 1.6.5 beta, Automated Primary Key Index Creation on Structure Saves, what does this mean, what does it do for me and do I need to be aware? 
I did look in the docs first, honest.
LOL....yeah, the docs have not yet been updated. That will be the last thing that we do so we don't have to "re-hash" anything. I made a change yesterday, which has not yet been posted, to default this value to True which will behave the same as it did previously.
When checked, the DDT will automatically create the primary key index when you save the structures (it deletes the old one and then re-creates it). The DDT has always done this, however, it always creates this as clustered. There are times that you may not want the PK to be clustered, so in this instance you would manually create the index and you want the save to leave it alone.