install a helper program on your PC first.
The program, which is aptly named Android File Transfer, provides third-party Media Transfer Protcol (MTP) support, which Mac OS X doesn't natively provide. MTP started off as a Windows Media Player technology, which is probably why Apple doesn't support it, but today it's represented by a standard USB device class and an extension of its precursor, PTP.
MTP support is definitely a step up as far as Android is concerned. Rather than 'turn on mass storage mode,' which locks local apps out of your SD card, MTP allows both the phone and the PC to access your phone's filesystem at the same time. Hopefully Medial Transfer Protocol will find its way to the smartphone version of Android in due course
Incidentally, it's possible that the upcoming version of OS X, Lion, could support MTP. If anyone has Lion, and a Motorola Xoom, we'd love to know if you've had any luck connecting them.