Mine is about 3-4 inches. That way the color of the painted walls shows and provides contrast. The tile back splash goes right up to the trim and abuts it. I'm pleased with the way it looks.

I've seen many beautiful kitchens on GW in which the cabinets butt directly against the trim. In others, there is a full six plus inches for a more "unfitted" look. (This is what I plan to do.) Do you want to see some paint or tile between your cabinet and window? I think that three inches is a nice compromise width to show a little "air" between the window and cabinet.

Three inches is probably what Christopher Peacock himself did in his own kitchen posted here:

Mine are nine inches away on either side. I questioned if they should be closer, but I'm happy I didn't move them any closer. It keeps that area (my sink is under the window) open and airy. Check the kitchen update II for pictures.

Since styles and personal preferences in window treatments vary over the years, you might want to consider clearance needs for various styles you wouldn't use today.

I think it depends on the size of the wall and cabinets.
And of course what you like.

Here are some ideas...
~boxerpups

We have a 48" window (plus trim) and we had the cabinets butt right up to the trim. But in our case we only had 6-8" to work with on one side, so we chose to have wine racks (wood, same as cabinets) installed on both sides. I think it looks nice, and otherwise I think I would have felt it was a waste of space if we left it open. And the wine cabs are not as "solid" looking as a regular cabinet w/doors.

Since there's not too much room above the window (and we have a valance and crown moulding w/ the cabinets) we plan on putting the same tile up there as our backsplash.