Thanks curt & whpalmer4.
Yes, I use the Start column most of the time but I was mainly referring to applying a Start Date to several Activities at once, hence the mention of the Activity Inspector Start field.
My reason for highlighting the need for an extension of the Availability Filter to include "Started" and "Started or Due", etc, is... like a lot of people, I use Start Dates to determine what I'm going to do today, so I don't want to see Actions that don't have start dates and that's not possible with many views. OF currently limits that possibility to Grouping by Start and then closing the "Start any time" group. Any other view is littered with Actions that have no start date. For me, that's a visual mess and limits the Perspectives that I can use. One of the salient points of Allen's GTD theory is to think about things once, during Processing, and then not think about it again until Review, so I don't want to have to turn Flags off and on... that's a clumsy solution.
whpalmer4, regarding the usefulness of auto-rollover of Action start dates, I don't see this as important as the need for more options in the Availability Filter. In fact, it's another possible work-around to solve the same problem. I agree, it's a binary condition... I want to see things as either started or not, but to view Actions with start dates I must Group by Start Date, and I end up with lots of groups with different sets of start dates... again a visual mess.
I want to be able to see just those items with current Start Dates in a variety of Perspectives. I think a lot of other people who are not power users might like that as well.