I am a firm believer that a good massage therapist and Yoga teacher should never stop training. Whilst every client teaches me something new, formal training is important too. I go to Thailand for a month every 1-2 years, with visits to other teachers in between. For Yoga, I attend regular on-going training with Yoga Scotland.
Here are a few certificates from courses I've been on. Bits of paper don't guarantee a good therapist/teacher (and some of my most knowledgeable teachers don't even give certificates at all!), but I understand that they can help give some reassurance to clients, and are necessary in some organisations for insurance purposes.