I've only had the setup in my signature for a month, but I've yet to see any problem with Time Machine backups on two MacBook Pros, one Snow Leopard and one Lion, both of which back up wirelessly every hour and are slept at night. But unlike the situation with the OP of this thread, our NAS has been on a UPS the entire time and has never lost power or been shut down hard, corrupting its file system. I've used both 2218 and 2219 OSes on the NAS.
As far as the Time Machine software itself, I've had it running 24x7 for four years on an internal drive in my Mac Pro at work, again, on a UPS. That included swapping it from a 1TB drive to a 3TB, use with Leopard, Snow Leopard, and Lion OSes, and a motherboard replacement. Pretty robust stuff.
DS 1512+ w/3GB, 5 x 3TB Seagate ST3000DM001 8.2TB RAID 6, half files/half Time Machine.
Icy Dock MB559U3S-1SB enclosure w/4TB Hitachi UltraStar via USB 3 for files backup
UVERSE to AirPort Extreme + 2 AirPort Express w/speakers. TRENDnet TV-IP312WN camera
CyberPower CP1500PFCLCD Sine Wave UPS
DSM 4.1-2661 w/SSH + SFTP, VPN Server, Syslog Server, Media Server, Mail Server, Mail Station,
Audio Station, Surveillance Station, Photo Station, Web Station - DS Apps on iPad & iPod Touch.