There hae been a huge increase in other things such as franking privileges over the last two years as well. From the WSJ:
Hundreds of lawmakers traveled overseas in 2008 at a cost of about $13 million. That’s a 50% jump since Democrats took control of Congress two years ago.
The cost of so-called congressional delegations, known among lawmakers as “codels,” has risen nearly 70% since 2005, when an influence-peddling scandal led to a ban on travel funded by lobbyists, according to the data… .