RORY  Thank you so much! The bug with Apple's layout was the main thing stopping me from really using Dvorak. I was afraid I had to give up hope on using Dvorak regularly, but now I can switch tabs in Safari without changing layouts. This is just what I needed. Sadly, it isn't perfect, because once in a while, Command-Shift-] in Safari will increase the text size (like Command-Shift-+) instead of changing the tab. But this doesn't happen every time, and usually doesn't happen when I open the Window menu first. Otherwise, this layout has worked fine for me.

By the way, two more little things for the developer: when I open the layouts in Ukulele, it tells me there are some control key combinations missing and offers to add them. Also, there is a typo in the readme: when saying the two possible paths you can install it to, you say "blah OR/ blah" instead of "blah or blah". Just tiny things you might want to look into.  
(Version 1.1)

COMPOTATOJ  Thank you! I tried this on Mac OS X Leopard and it fixes all the problems I was having with Dvorak - Qwerty ⌘. I have no idea why Apple doesn't fix this. I highly recommend this to anyone who uses Dvorak on the Mac.  
(Version 1.1)

MATTHIAS215  Although I'm sure the fact that few people will need this system mod because, well, few people know the dvorak layout, those of us who are learning to use Dvorak after years of QWERTY will find this infinitely useful. The biggest hurdle for me learning Dvorak really has been that my fingers automatically jump to the "real" shortcut letters as I type. This program has been a real help in that regards, and since it's just a small system modification, there's pretty much no chance of bugs (at least from 10.4.8, when I started using it).  
(Version 1.0)