Investors can't seem to get enough of China. In their U.S. debuts Wednesday, Shares for Youku.com (YOKU), the region's No. 1 online video site and called the "Chinese YouTube," jumped 161%, while E-Commerce China Dangdang (DANG), called the "Chinese Amazon," shot up 87%. It's a land grab, as investors want early stakes in China's online ad and commerce markets, says Dennis Wassung, associate portfolio manager for Cabot Money