As with all crypto-currencies, WUBs have value simply because people believe that they have value. Everybody needs to decide for themselves what value a WUB has to him or her. These days, most currencies aren't backed by anything anymore, except by the (justified) belief that they will be able to be exchanged for something else (eg. food, shelter, etc.) in the future.
So what can WUBs be exchanged for today? At the time of writing, WUBs can be exchanged for entrance, drinks and musical real-life wubwubs at the Stefan K.K. headquarters. The rate for a one-hour performance (drinks included) fluctuates daily, but at the time of writing the rate is around 1 WUB for a one-hour performance. This is in addition to the benefits and functionality provided on the official WubCoin website.
(Art by MikoWorks)