I think what Halldor means that it is counterintuitive to
> have the weekday labels positioned at midnight. The
> attached example figure shows a week's worth of data, and
> from a quick glance you'd imagine that the peaks occur at
> night, while they really are in the afternoon. Aligning
> the labels' left-hand side with the ticks would help a
> little, but not nearly as much as having the labels
> centered between the ticks.
If so, this seems less a problem of tick alignment than tick placing.
One can easily construct ticks for noon.
import matplotlib.numerix as nx
from matplotlib.dates import date2num
dmin = date2num(datetime.datetime(2003,05,10)) # in days
dateticks = nx.arange(dmin, dmin+7)+0.5 # 7 ticks, at noon
xticks(dateticks, rotation=-45, ha='left')
It seems to me that you want the tick labels clearly associated with
the ticks, and you should place txhe ticks accordingly, but I can see
how there is room for argument...