For communities that have a functioning economy, where it is partly the economy that defines the community -- like, say, a group of people in the same nation state trading with one another -- I think it's quite unusual to see that in terms of buying power within the community. I.e., the currency might go up or down versus other currencies, but in terms of local buying power, I would have guessed it's more often trending up or trending down rather than bouncing back and forth. Where it does start suffering too wildly, I think historically the 'solution' has tended to be either replace it or peg it.
IMHO, top-down price controls rarely work out, but as for more trade -- more merchants accepting it, more consumers buying with it, etc. -- that seems like a winner to me. Also, I know I'm frequently banging the derivatives drum, but for businesses to handle any significant volume of BTC is going to require more effective hedging mechanisms than just converting BTC to fiat as quickly as possible. What business wants to bear additional risk without some kind of potential benefit to counterbalance that risk?
I'm guessing that most assets which are both relatively liquid and standardized -- as gold is, at least in coin form -- could be viewed as a decent way of moving USD around. Gold in bar form introduces higher assay costs, reduces liquidity, etc., but even then it could serve the purpose. On the face of it, it's not necessarily a great way of doing it, since storage and delivery costs are significant, but I suppose it depends on the goals of the person wanting to do it.