Partway through the P'sukei d'Zimra section of the morning service is Psalm 100 (Mizmor l'Todah). Many, but not all, people stand for the recitation of this particular psalm. Prayer books vary, either not mentioning standing, saying that some people stand for this one, or like Artscroll, simply say "Psalm 100 is recited while standing".
Why is this psalm different from all other psalms? Where is standing for it mandated? Broadly, who follows it and who doesn't?
I have seen Ashkenazim who do or don't, Sefardim who do or don't (but my sample set of Sefardim is very small), Orthodox who do or don't, Conservative who do or don't. I cannot tell if this breaks down on geographic lines, ideological lines, or just people who don't want to get up for such a short period.