Chucktown can tell you about the bodywork and the horror stories. I think other items are more hit or miss. If it is only a cosmetic part ie... bar end or even a wind screen then maybe. If it is structural or safety critical like a brake part I would not stake my life on the quality. I've bought some non motorcycle parts from China that were ok like the carbon water bottle cages for one of my bicycles. Lot cheaper than big name domestic and worked just fine. Always look at the seller ratings.
Japan is a bit different. Simon always has top flight stuff and frequents the forums. I would kill for some of the Ladybird exhausts he has from time to time. He is on Ebay as Simonkobe i think...
'04 Nicky Hayden
Flapper/PAIR Mod-Ladybird Full Ti Moto-GP -w- Long Cans-Proton Flushmount LEDs
HotBodies Undertail-Tyga CF Hugger-HEL Lines
Custom plate mount w integrated LED brake light
15/41 gearing-PCIII USB-Speedohealer-Carbone Lorraine Pads
Spencer Seat mod-Ceramic dual coat headers
It is a wise man who knows where courage ends ...
and stupidity begins.