I'm using it at work on a daily basis almost. Their expense + flight / hotel booking system is surprisingly OK relative to enterprise software, they also have a mobile app which is pretty great.

It's quite a complex topic, lot's of corporate policies to enforce, and basically they had to develop all the tech facade that Kayak, Expedia etc have (flight and hotel booking) as well as a lot of financial logic for expenses.

There is a lot of money in enterprise software... I wish more YC startups would tackle that area...