You are regarded as a responsible netizen when you imbibe the habit of leaving out-of-office messages. For employers and HR managers, it is worthwhile to teach this practice to your employees. Out-of-office emails show that you are polite and professional, lending credibility to your corporate culture.
Dear Customers. We, the employees of this office are going to take our days off from the 25th of December to the 5th of January 20XX in lieu of Christmas and winter vacations. Your needs are Supreme to us so one of our representatives will be available 24/7 in case of answering any query you may have. Feel free to contact us on the following number [X].

I think that it depends on whether or not that OoO was going to people in the company, who new your personsality and would appreciate the humour/personal touches, or to everyone, always. If I got the from OoO from a quirky co-worker, fine. It I got it from an outside contact that I have had little contact with? Unprofessional and a bit off-putting.
Over time, I began to suspect that those who might be telling the truth (of which I suspected there were very few), would mention their relationship to the person and possibly the cause, for example “My grandmother just passed away after surgery.” The ones who left it wide open (“someone close has recently died”) led me to imagine that it could be a random person in their city that they read about in the news, their goldfish, or perhaps a distant relative who had passed away in the previous few years.