Dan - I agree 100%. That's why when I speak to topics such as audio equipment, scuba diving or auto racing (to name a few)...I rely on my real world knowledge of these "hobbies". Such as collecting audio equipment since I was 16, or racing professionally in the SCCA, or spending countless hours at the track setting up race cars, or being liscensed as a PADI Advanced Open Water Diver, diving wrecks, deep dives, night dives and navigation dives with a compass.
There are a few where I consider myself an expert. But there are many others where I would not consider myself an expert, just very informed.