Here's another tip (although Max probably knows this one): You can use large PPATs (like 128x128) in a theme and avoid the 'stutter' effect that you'll get in certain windows (like System Prefs) as long as you make sure the first 8x8 upper left pixel region in your master PPAT is uniform enough to tile in a visually consistent/pleasant manner while not standing out in the larger master PPAT. The system will tile this region over very large and seemingly important expanses of the interface, go figure...
Another tip (or something I've been doing anyways)... you can get pretty thick pane borders if you make the pane fill nothing and incorporate a suitable edge mask into the pane border so it blends with any underlying PPAT fills. The only place I've seen this not work is with Metal Windows, which don't have a specific pane fill resource of their own, they just cut into your Pane border enough to utilize the outer stroke and shadow region of the original Aqua Pane resource... it doesn't look bad, but you can compensate by moving any beveled Pane edges you want visible in a Metal Window into those regions occupied by the Aqua Pane stroke and Shadow.
And a design tip (which can be ignored): Aqua's 'sculpting' exists primarly in the vertial space... horizontal real estate is hard to come by and any implied outer edging depth through beveling, etc will fall apart with titlebars meeting dropdown toolbars, lack of right/bottom edging in menus, etc... any theme that utilizes substantial edging detail will look wonky as a result in many cases. In themes that use some sort of defining bottom edge in a titlebar, I would suggest keeping edging down to 1 or 2 pixels width... in those without a titlebar bottom (where the implied effect is a continuous vertical surface), edging is best avoided altogether or faded top to bottom in some way so that abrupt transitions between things like the finder titlebar don't happen. If your theme requires depth, there is too much vertical real estate in the Aqua titlebar definition anyways (visually, it's too tall in comparison to the other window elements like scrollbars), so explore implied depth through vertical edging effects and your results will sing better with the overall limitations of the theme... same is true of tabs, which are way too tall. You'll find that you can maintain consistent edging throughout the majority of the design if you limit your major depth-enhancing effects to the vertical plane. Does that make sense?
Another tip (or something I've been doing anyways)... you can get pretty thick pane borders if you make the pane fill nothing and incorporate a suitable edge mask into the pane border so it blends with any underlying PPAT fills. The only place I've seen this not work is with Metal Windows, which don't have a specific pane fill resource of their own, they just cut into your Pane border enough to utilize the outer stroke and shadow region of the original Aqua Pane resource... it doesn't look bad, but you can compensate by moving any beveled Pane edges you want visible in a Metal Window into those regions occupied by the Aqua Pane stroke and Shadow.
And a design tip (which can be ignored): Aqua's 'sculpting' exists primarly in the vertial space... horizontal real estate is hard to come by and any implied outer edging depth through beveling, etc will fall apart with titlebars meeting dropdown toolbars, lack of right/bottom edging in menus, etc... any theme that utilizes substantial edging detail will look wonky as a result in many cases. In themes that use some sort of defining bottom edge in a titlebar, I would suggest keeping edging down to 1 or 2 pixels width... in those without a titlebar bottom (where the implied effect is a continuous vertical surface), edging is best avoided altogether or faded top to bottom in some way so that abrupt transitions between things like the finder titlebar don't happen. If your theme requires depth, there is too much vertical real estate in the Aqua titlebar definition anyways (visually, it's too tall in comparison to the other window elements like scrollbars), so explore implied depth through vertical edging effects and your results will sing better with the overall limitations of the theme... same is true of tabs, which are way too tall. You'll find that you can maintain consistent edging throughout the majority of the design if you limit your major depth-enhancing effects to the vertical plane. Does that make sense?