Well, Mercury retrograde is typically a time when you can expect a lot of delays, technology and appliances breaking down (for instance, in this year's retrograde, my Macbook's graphics card decided to stop working out of the blue and now the whole computer has to go and be repaired), oh, and mishaps and misunderstandings with communication.
If you practice any kind of occult magick, you'll have to make sure your intentions are even clearer because Mercury could mess with you and give you something wonky if you aren't clear enough. Also, I'd avoid making any big ticket purchases at this time, and I'd also allot extra time when traveling, because you can typically expect delays.
That tends to be the general experience for most people, however, it's been said that certain people are more susceptible to this retrograde than others, largely based on planetary positions in their natal charts.
