If you haven’t caught the news from one of your usual sources, BlackBerry Media Sync for Mac is now available in a preview version. (It works just fine for me, though – OS X 10.5.6, Bold, 8GB microSD card and a ridiculously sized iTunes library of 25,682 songs.)
One option I’d suggest avoiding (depending on library/media card size) is the “Automatically fill free space” checkbox. Due to the way that the onboard media player parses files, a lot of single unrelated tracks can cause a lengthy initial parse time on the device. This wait may have improved since this build was released, but I’d suggest creating a Smart Playlist or two before using this utility.
I honestly didn’t expect to see this program released until the new year, but it’s awesome that it’s now available to the general public. Hope it works for you!