This weekend I removed the injectors from my 2002 Golf (ALH), with 95,000 miles, so that I could put the nozzles in my jewelery sized ultrasonic cleaner. I didn't really have any expectations, but just wanted to give it a try and let others know in case anyone else has been interested in the idea.
I wouldn't say I've noticed any differences in performance or anything. When my next tank of fuel runs down I can report back if fuel economy changed. I just put each nozzle into the cleaner for about 6 minutes and the fluid I used was regular Fuel injector cleaner that you can get from any parts store. There was some buildup of carbon on the injectors, but none really around the tip.