In reply to Martin W:
I found spinnaker tape way better than duct tape - if applied well - cut rounded patches, apply to flat clean surfaces and most importantly, really rub it in to get a good stick. Work from the inside of the patch outwards, rubbing hard to mesh the adhesive to as many fibres as possible, and the friction heat provided helps with the seal.
I've used tenacious tape, it's also good, its popular and slightly easier to use. I prefer spinnaker tape personally.