Andy Polyakov's page at http://fy.chalmers.se/~appro/linux/DVD+RW/
should answer all your questions. Don't be misled by the DVD+RW part.
He knows what he's talking about and that includes all DVD formats.
Just scroll down to the tech section.
The quick answer is yes. Actual user data capacity is more like 4.4 gigs on
a single-sided DVD plus re-writable.