According to this MCV piece, the first six months of 2008 have been the biggest ever. The news comes from Chart-Track, so that means no figures, unfortunately.
“In terms of overall software, including non-games, this is by far the biggest first half of the year ever,” said Chart-Track director Dorian Bloch.
There's no other info through the link, as Chart-Track doesn't allow anyone to publish actual numbers. Sorry about that.