not sure what you mean here exactly - you don't like the look of the cursors we use ? In that case, choose a cursor theme that you like better.

Or do you mean we should be using a different, widely available cursor for these cases ? I don't see col-resize and row-resize in the cursor themes I have available around here...

Compare these cursors:
sb-h-double-arrow http://www.rw-designer.com/cursor-detail/345
col-resize: http://webdesign.about.com/od/styleproperties/ig/CSS-Cursors-Gallery/col-resize.htm

col-resize is what is used in e.g. Qt for the things i named in original report, while GTK uses sb-h-double-arrow, which doesn't look like correct cursor choice.
You can find col-resize cursor in e.g. oxy-white cursor theme. Also, it should exist in X default (fallback) theme.

Ok, this is useful information there.
Putting a reference here and retitling:

http://dev.w3.org/csswg/css3-ui/#cursor

Created attachment 303168 [details] [review]
Use standard cursor names

This changes GTK+ to use gdk_cursor_new_from_name() with the
'standard' css names, instead of GdkCursorType.

This needs to wait until all backends support the css cursor names.

Attachment 303168 [details] pushed as 5c2759a - Use standard cursor names