For reports, the default column widths appear to be a percentage of the window width. This is less than ideal on a maximized window, where (for example) there might be category names up against the left edge, with their values all the way against the right edge. I can manually adjust the widths, but I have to do it for nearly every report (and most times when I change the grouping on a report). That gets annoying.

(also, for un-grouped reports with only two columns, I can't adjust the right edge of the rightmost column at all. I think that might be a bug, since it works in grouped reports)

I suggest a different default: For most columns, size them to accommodate the widest string in that column. If the columns are part of a group (e.g. group by month), use the widest string in any column within the group (so that they're all the same size). I think this is how it already works when there are too many columns to fit the window, although it doesn't seem to account for currency symbols when calculating widths.

If the user changes the column widths, allow them to revert to the default by double-clicking on the column's drag handle.