Extreme Work Pressure
There is definitely pressure to get things done for the holidays such as Greeting Cards, holiday promotions and more, but the real issue here is time management on your part and your client's part. If you know a client does a yearly promotion or greeting card, call them earlier in the year and ask them to start planning now so the end of year rush doesn't have to be so hectic. Training your clients to respect your time is just as important as managing your end of year projects, and yes I do mean training your clients. It's important that they know how to work with designers, especially when it comes to time sensitive projects like Holiday Greeting cards or product promotions they need to have out before Christmas.
Many clients do have unrealistic deadlines towards the end of the year, but this goes along with the previous note. Training your clients to give you design work early can save you from having to deal with 1 day deadlines and overbooked printers. Remember, the early bird catches the worm! The blogger on Graphic Design Blog talks about getting a calendar design out in a day: this is the point at which you kindly tell your client that this is impossible and next time, they need to come to you earlier. If you're professional about it and explain to them that rush jobs come at a two-fold price: lack of quality and a fee, they'll soon learn to give you graphic design projects earlier and with a fair amount of time for you to do the project and produce quality work within their budget.
No Time for Family
This is unrealistic. Obviously your clients will be spending time with their families, and they should expect the same of you. This can be fixed by simply saying no to projects that you know will eat up your precious holiday time with family. If your client can't understand this, then you probably don't want to be working with them. Moreover, along with the last two points, if you manage your time, and help your clients to understand how to manage theirs, you'll be able to get projects done before deadline and have time to spend with family afterwards.
Clients Demand Perfection
I have nothing else for this but one sentence: don't they always? Christmas should be no exception to this rule or issue that designers face. The blogger talks about clients demanding so many revisions it's hard to keep up, but the simple issue is this: are you saying no to these minuscule revisions? If the scope of the project has gone far and beyond the original contract, are you charging more for your extra time spent? If not, this is an issue with your process and not Christmas.