Hi Star!
We're still hacking on the Mac OSX IDE ("Coming soon!); we've proven every piece of functionality but haven't pulled it all together into a binary release package yet. Right now I believe there are issues with extracting large binary dependencies from the mysterious external maple-ide-deps-macosx-0018.tar.gz file we host at static.leaflabs.com; the dfu-util binary doesn't get copied correctly giving the above error. The first step to fixing this problem is the arduous task of recompiling the codesourcery arm-none-eabi binaries for the OSX platform. There are a number of automated ways to do this but we ended up having to do it over by hand to work with the Maple, and we have to tweak that process to generate 32bit-compatible binaries now. We're really embarrassed about the complexity of the entire IDE build chain, what with all the external dependency blobs and many build scripts; the main Arduino IDE finally switched to an ant build process and we look forward to merging those changes in.
Re: the name of the IDE, we still think of the Maple IDE as a minor tweak to the Arduino IDE as opposed to the monstrous thing it has grown in to. Really the Maple should just be one of many target boards in the regular IDE, and with any luck that structure should be possible after the forthcoming Uno Punto Zero refactoring of Arduino (http://arduino.cc/blog/?p=392). Until that point we've stuck with the hybrid title.
Sorry about the delay in a stable software release; power has been out in our office and we've been filing orders and hacking compiler compilers by lamp light the past couple days!