As a business owner, one of the most important things for me, is to keep a good relationship with my clients.
I believe receiving a holiday greeting is always heart-warming: sometimes it makes you laugh, sometime it makes you all teary-eyed, but it always makes triggers some emotions.
Anyway, don't forget to take some time before each holiday to design your greeting and send it by mail, or email.
Remember, to save some time, block a time to batch-create your greetings. Save them so you don't do it at the last minute or forget about it...