Ian,

Not horror stories, but a lot of extra coding to get around problems with...
1. SQL commands opening tables and leaving them open in various work areas
2. Long SQL commands break because they exceed the 256 character limit (or 512, I forget)
3. Problems with diacritics (data that contains quotes or double-quotes)

In the end it wasn't worth it unless we were sure the customer might start using some sort of RDBMS like SQL7. Then we could pretty easily upsize the app to work with Oracle or SQL7, etc...

Just my opinion!