>If a connection is already open, does a DataAdapter close it & reopen it? Does the DA close it in all cases, or only if it opened the connection?

AFAIK, if it's open, it's left open. It leaves it in the same state as it was passed in. So if it's not open when you call the DA, it will open it, fill the data, then close it. If it's already open it will use the open connection (and leave it that way when finished).