ibprs500 0.3.5 is working for me on Mac OS X 10.4.8 on a Macbook Pro Core 2 Duo 15".
Code:
Macbook-Pro:~/Sources/sony/libprs500/trunk scotty$ prs500 infoDevice name: Sony Reader
Device version: PRS-500/U
Software version: 1.0.00.21081
Mime type: application/x-bbeb-book
Macbook-Pro:~/Sources/sony/libprs500/trunk scotty$ prs500 ls /
Data etc mnt opt1 sbin var
bin home opt proc tmp
dev lib opt0 root usr