I take it that ".dataTable" is supposed to be the class of the table element, and replaces the ".display" label used in the demos. I'm fine with it being different than the demo .css, but ".dataTable" is easily confused with the ".dataTables_xxx" classes assigned by default to other elements. Also, in the real world, when ".dataTable" needs to be replaced, guess what happens when you use an editor to perform a global change of ".dataTable" to ".userTable" -- all the ".datatables_xxx" selectors are incorrectly altered as well. I would suggest using a name as simplistic as ".myTable" or even ".myTableClass" if you really want to highlight this is as a user-defined field.
My second question relates to the ".DataTables_sort_wrapper" and ".DataTables_sort_icon" classes: is there some reason these are capitalized differently than all the other class names? The CSS standard is case-insensitive, but the XHTML standard is not. (This isn't strictly a 1.9 issue, but if you were to make a change, this wold seem like a good time...).
My last question relates to the ".paginate_xxx" definitions: are these actually used in a jQuery-ui themed app? I know the background images are supplied by jQuery-ui, not these defined here. (I haven't tried full-number pagination, so maybe they are only needed then?)
Again, I appreciate the effort, but as someone for whom using DataTables is their first effort with a product which generates HTML/CSS, keeping things as pared down as possible is a real help when debugging my own work.