I can attest that building themes are a royal PITA due to the reasons Bil outline in his post Site Settings, Apply Theme, Apply, Lather, Rinse, Repeat.
Bil has taken it a step further and provided an idea for a simple web part that makes this process go a little easier. Check it out.
Now all we need is for Bil to provide this little ditty for us complete web part morons so we don't have to build it. :-P Hint, hint, nudge, nudge, say no more.