I love it! "Norton Commander" interface, the split window style, is a wonderful way to browse - and manage - your filesystem. Total control, indeed.
I love the shortcuts: F8 will delete things, holding shift auto-selects files in the list and copy/paste, duplicate stuff and making new folders is so simple.
And it's beautiful, too! I really appreciate that muCommander is both cross-platform and available in a portable (USB stick) friendly version: Next time, while tweaking a new Linux distribution, I know which app I'll download after the first boot :-)
Oh, backspace takes you back in your filesystem. And Enter (Retun) will do that thing switchers (and experienced OS X users, too) miss in the Finder: Opening a file or folder.
Cross-platform, an application that's sort of its own iceland, but yet integrated with OS X in a nice way, updates at least once a week... Finder + muCommander = a pure Mac OS X experience, always ready to drop some heavy files, lifting and re-organize thousands of files or cleaning the desktop in a flash.
And well, it's free too :-)