How long do you keep documents for?

The IRS recognizes digitized copies as originals:

http://www.irs.gov/pub/irs-irbs/irb97-13.pdf

SECTION 7. DESTRUCTION AND
DELETION OF ORIGINAL BOOKS
AND RECORDS
This revenue procedure permits the
destruction of the original hardcopy
books and records and the deletion of
the original computerized records (other
than ‘‘machine-sensible’’ records required to be retained by Rev. Proc.
91–59, 1991–2 C.B. 841), after the
taxpayer:
(1) has completed its own testing
of the electronic storage system that
establishes that hardcopy or computerized books and records are being reproduced in compliance with all the provisions of this revenue procedure; and
(2) has instituted procedures that
ensure its continued compliance with all
the provisions of this revenue procedure.

While the IRS does accept digital copies, I'd be concerned that they'd claim they were subject to alteration and refuse to accept them.

Not too long ago, my accountant was telling me that he just had an IRS agent who questioned the authenticity of every document he was given . . . and they weren't copies or scans, they were the original documents.

He highly recommends to me that I keep originals even if for nothing else but to cut down on the potential hassle factor with the IRS. Not to mention is saves us plenty of time with regards to scanning in all our paperwork.