A buyer gets his sallary in dollars/euros/whatever. Then he converts it to bitcoins. Then he buys something in bitcoins. Then the seller cashes out the bitcoins into dollars/whatever again.
This is a complete dollar -> bitcoin -> dollar cycle.
If this was the main use of bitcoins (for the time being, it isn't), speculation would be somewhat limited. It would also expand the number of people using bitcoins. Let's face it, bitcoin is just another currency in the world, a very small one so the main use, apart from speculation, will be something like the cycle I described.
I thinkwe should all create local groups and meet together to support our cause... by convincing local shops to accept bitcoins (and teaching them how to use them) and buying things on those local shops. Meetings would be in bars and restaurants that would accept bitcoins. We should all buy everyday things with bitcoins. If we are willing to buy, sellers will automatically follow.
I say we should start convincing sellers by trying to buy somewhat expensive things with bitcoins. For example if you want to buy a guitar, buy it with bitcoins.
Perhaps speculation will be a predominant factor in the bitcoin economy, but bitcoins won't become a real currency unless people use them to buy stuff. I say we go local.