Have 2 WD Green 2TB HDD's in RAIDO mode in my Synology NAS. No issues so far. Bought them as external HDD from Warehouse Stationary but ripped apart the casing carefully and have been using them for 6 months or so without any faults.
Switching to Seagate 2TB 7200RPM's now though for future use as they are just as cheap and faster!
Right now I have 4x2TB and 2x3TB WD Caviar Green drives of varying ages (maybe a few years on some 2TB). No problems at all. The 2TB drives all came out of external enclosures, was cheaper for me that way.