I just downloaded and installed "USB Storage for SL 5500/5000" from Killefiz and I'm impressed. I plugged in my cradle and Z and started the "USB Storage" app in the Z's settings and on my desktop appeared my SD card. Pretty slick.
This is cool because I can leave my SD card in the Z and file transfer this way.
Off the subject, but I posted my experiences with MyStep/MyPDA on my blog.