Gibbons are awesome. They are cute, amazingly acrobatic and somewhat comic looking. They aren't, however, meant to be pets or toys. Over the past decade, illegal trade in wild gibbons has increased in Thailand, with most of the animals being used as entertainment in bars or hotels, or even as props for photographers who roam the streets outside of night clubs luring people with their cute baby gibbons to come take overpriced photos.
The backstory is never a pretty one. How the gibbons came to be owned by the hotel/bar/photographer is usually shocking and always involves some law breaking. So, whenever someone tells you that they "rescued" a gibbon and that's why it's living at their hotel or bar or even elephant farm, keep in mind that the story is a load of garbage. In Thailand it's illegal to own these animals as pets and that there are plenty of legitimate rescue organizations that really do rescue gibbons and don't use them to lure tourists or make money.
One of those organizations, the Gibbon Rehabilitation Project in Phuket, also gives visitors a chance to see gibbons in a totally legit, ethical environment (the gibbons you can visit live in forest enclosures and are just beginning the rehabilitation process). So, if you're in Phuket and you want to see some gibbons, skip the photo op with the dude walking around with a baby gibbon on his shoulder and head to the Gibbon Rehabilitation Project instead.