Just got a message from WD saying there is a risk of data loss if you use their software manager and drives.
From the community forum (I doubt they will mind it is copied and pasted as this could be very serious for some users).
There are reports of Western Digital and other external HDD products experiencing data loss when updating to Apple's OS X Mavericks (10.9). Western Digital is urgently investigating these reports and the possible connection to the WD Drive Manager, WD Raid Manager and WD SmartWare software applications.
Until the issue is understood and the cause identified, WD strongly urges our customers to uninstall these software applications on their systems before updating to OS X Mavericks (10.9), or delay upgrading. If you have already upgraded to Mavericks, WD recommends that you remove these applications and restart your computer. WD has removed these software applications from our web site solely as a precaution as we investigate this issue.