The max draw for the ws2801 strips from GreeLED is 2A per meter, that's full white all led's on.
The ws2801 strips you posted from Ebay are from GreeLED as far as i can tell and they are about $12.5 per meter.
Wish i knew that before i spent $90 on 3 meters about 2 months ago on ebay. Found the manufacturer after I bought mine.
Also, I ran into an issue powering my Mega boards from my Laptop. The led's would be erratic and not function properly, as soon as i changed USB to another device, a desktop monitor with USB it worked just fine.