I have been lurking for several days now and have also purchased one license to try out. I own several vB licenses and have been dissatisfied with the product since being forced to repurchase all the licenses to upgrade to the much touted 4.0. 4.0 has not met expectations.
I am not, however, dissing vB as they do offer many mods and customizations that I have found vital for running my forum based RPGs. The primary one is being able to have multiple accounts and switch easily between them for those of us writing several character roles.
Recently, I have discovered a dedicated RPG management and writing system that also allows for multiple characters on one account, etc. As I cut over to using that for the actual gaming portion, I am downgrading the forums to be strictly chat and planning, hence trying a Xenforo license to see how well it works for our needs. There are two or three features/mods we desperately need so I hope they come about in the future. I am also waiting on a skin to be modified to work with Xenforo, once that's done, I'm cutting my already converted game over to XF.
Now...with the background out of the way...
I am very impressed. The Admin CP is easy to use although I need to familiarize myself with the differences in terms between vB and XF. All I can say is, if you keep up this level of quality and customer service is also comparable...you will eventually sell me at least two more licenses.