After two days of running after updated to firmware version 1.67, still decide to switch back to dlink firmware (Dlink-624+). Although the new USR firmware doesn't crash, the wireless connection speed is not stable. Initially, I can reach the speed of 36-48 Mbps, while this morning it drops to 1 Mbps, sometimes it will raise to 12 Mbps, still there are undeterministic delays. Overall, Dlink firmware is much stable and thus better.
Remember 4 years ago I got a 3COM home connect router. The router was so bad and I lost my faith to 3COM at all! I hope this isn't another case for me to lose confident to a respectable company.