The "Summary" of a service record is intended to be a terse description of the highlights of progress and problems, focusing on what remains to be done. Ideally the reader shouldn't have to consult all of the transactions and from that attempt to deduce what remains to be done, and what the fundamental problems are.
When work is recorded as stalled, the reason for that should be mentioned in the Summary. When work has become overdue, any problems that caused should be documented as well.
Estimated time to completion can be recorded as well, if time worked isn't being tracked. If work time is tracked, then the total time estimate is better placed in the cost estimate field.
An example of a style that's been used is timestamped single sentence descriptions of highlights, e.g.
2003/09/15: documentation remains.
2003/09/15: setup for Math hosts not done.
2003/11/06: lowered in priority; other work competing.
2003/12/18: other work still competing.
When specifying this field in a customized sort or display, any of the names "summary" or "Summary" can be used.