I am a customer who switched over to IPB about 4 months ago. Before then, I was a very loyal vBulletin customer.
What can I say about IPB? Well, the software is awesome. It is easy to use, I love the admin interface and quite frankly -- it is way easier to skin than vBulletin. The permissions system is abundantly easier to navigate and set compared to vBulletin. The promotions systems also easier to set. And did I mention that it's easier to create a custom skin (or theme)?
The community is awesome. I have also found that there are many talented designers and a plethora of skins and graphics to choose from.
Anyway, that's my opinion. I have a vBulletin license and an IPB license. I am actually considering to sell my vBulletin license for a second IPB license... even in the wake of the vB4 release.
