Yeah, Weight Weenies is great for getting an idea of the ACTUAL weights. Most of the readings I get from my digital scale are pretty close to the averages for the same product. The Deore cassette weighed in at 409g (yikes!) and the SRAM was 228g, both with the lockring.
Someone should build a bike and keep track of the CLAIMED weight versus the ACTUAL weight...wonder what the percentage is? Well, it will definitely depend on the company. All of the recent SRAM (X.9 shifters and derailleur, Avid SD SL brakes) stuff I have gotten has weighed exactly (to the gram) what it was claimed to weigh.