IMHO, PSD really isn't the best format for theme templates. Aside from the fact that Photoshop is expensive software which many people can't afford, vector graphics (particularly SVG) make modifications much easier (e.g. batch color replacement/shape adjustment, infinite scaling). Have you tried Inkscape?

The free development theme for earlier versions of Maemo (Plankton) was made with Inkscape, and Nokia provided the SVG template in the source package. Hopefully they'll do that this time around too, but I think Plankton is no more, and I'm not sure what its replacement is called.

edit: Btw, nice work on the theme joppu!