Hi Charles,
>>A questionable backup seems almost worse than no backup
>>since it gives a false sense of security.

Very good point. All I can say is that in my particular situation, I will be running the backup primarily at night when few or no users are on which minimizes the chance of an error. You are right that an error could occur, and in general I agree that a "false sense of security" is a very bad thing, but in this case I think it is better to be able to make the backup than not make it at all, particularly since the backup will usually be good.
I suppose it would be possible to test the backup by unzipping it using the copy and opening every table. That would at least ensure that the tables could be opened. It would not guarantee relational integrity in the event that the copy were made in the middle of a transaction. For that kind of certainty, you either must have the database in exclusive mode or be using SQL Server or some other back end. (I decided I could not wait to get the database in exclusive mode to make the backup.)
Regards, Chaim