QuickBooks is written to prevent the export of data
into other programs in a what that would allow them to supplant the "add-on"
features that Inuit wishes to sell.
For example, Transaction data can not be exported
at all. A Transaction Detail report allows most transaction data to be saved
in a comma delimited ASCII text data file but when selecting fields for that
report, you will find that customer address and other critical information
is just not available.
Also, custom fields like email addresses will not
be available unless they are added to the form that is the default for that
transaction type.
http://www.intuit.com/support/quickbooks/faqs/docs/w_cusfield2.html
last paragraph.
Intuit has also prevented integration of programs
that seek to add information to your existing accounting data by setting
up the import in such a way that if an item already exists, rather than modifying
only the fields specified in the import file, the entire item is first deleted,
then the import data is added in its place.
http://www.intuit.com/support/quickbooks/faqs/docs/w_importinglists.html
Questions:
See also: