The g'mara on Moed Katan 23a says that after shiva, when the mourner stays at home, he can return to shul but does not sit in his usual seat. (According to this g'mara, he returns to his usual seat a week later, or R' Yehudah says two weeks.) I haven't paid close attention, and anyway people in my community are not particularly attached to specific seats. Is this the custom today, that a mourner makes a point of sitting elsewhere after shiva? If it is not the custom today, when did it change? If it is the custom in some communities but not others, in which ones is it the custom?
When I was an aveil (for each of my parents), I changed my seat for the entire year. That is also the general minhag in my shul. This included Shabbosa as my new seat became my makom kavua for that year. After the year I returned to my normal seat.
Our shul is somewhat "Yeshivish" on the East coast of the United States (Baltimore). I consider us somewhat to the right of middle (though I would suppose that everyone considers himself in the center).
I attend a Conservative shul. This past year, I noticed that 3 families of mourners all sat in different places in both the the Shabbat shul as well as the weekday chapel. As a matter of fact, the rabbi presented a se'udah shlishit shiur a few months ago explaining this minhag to everyone.
Adding to this - During the year that I was mourning for my mother, I changed seats in the "large" shul on Shabbat. Until, the rav informed me that one should not display public mourning on Shabbat. Though, he had a "caveat" to this. Most of the congregants are occasional attendees on Shabbat. So. most others wouldn't recall someone's "regular" seat, and thus would not recognized if they sat elsewhere. As I am the Torah reader and sit in the same place each week, people would notice a difference. So, while some congregants can do it, I can't.
However, when davening on weekdays in the "chapel" (small shul), I did change seats.