The calendar accessible by clicking on the clock applet from
gnome-base/gnome-panel always displays the first day of the week as Sunday,
regardless of locale. (Most of the world has the first day of the week as
Monday.)
There's a patch on the above URL that fixes this; however it's not going into
Gnome 'cos of feature freeze and the fact that the calendar control will be
fixed in gtk+-2.4 (which stable users won't be seeing till Gnome 2.6); it'd be
nice to have this in the Gentoo ebuild; regardless, I'm posting this bug anyway
just to get it in the open.
I'll put up a patch that applies without fuzz (probably with some offset) to
gnome-panel-2.4.2; I'm not fussed if you choose not to apply and have to maintain
it.