no its not. you put your 'marked' 100$ in the laundry service and you get 100$ that came from some random dude. Assuming the laundry service doesn't keep logs (very big assumption though) the money that came through such a service can't be used to identify anyone
Logs are critical for this tracing to work, without them the trail ends. I was looking over Bitcoin Faucet and it does appear that, at least, they log all ip address. Then I made my way to http://blockexplorer.com and was able to trace all those block.
In the end, BitCoin is only as anonymous as you make it.
