Hoarding explained in 3 easy rules
1. Do exchange your USD for BTC.
2. Do NOT exchange your BTC for USD.
3. Only spend your BTC on sellers you believe follow rule 2.
Disagree with number 3. It's better to just ALWAYS pay with Bitcoin wherever you can, as it helps stimulating the Bitcoin economy and usability. Even if the merchant happens to convert it to EUR or USD. However, whenever you spend bitcoins, immediately buy back the same amount of bitcoins through an exchange. This way, you: 1. effectively keep your stash of bitcoins, and 2. you compensate the market supply/demand in case the merchant happens to convert his bitcoins to fiat.
Remember, Bitcoin is still in its infancy. We can't expect mainstream merchants to keep bitcoins, since they typically cannot pay their expenses and staff in bitcoins either. By ignoring merchants who don't keep bitcoins, you're sticking your head in the sand. By paying them in bitcoins,
even if they convert it to EUR or USD, we help them getting into the migration phase. Once they notice how they can spend bitcoins everywhere, their urge to convert to fiat will diminish, and we'll grow towards a 100% Bitcoin situation.
It has been mentioned before: hoarding / hodling and spending bitcoins go hand in hand very well.