So:

Long term - (several years) upward trend, assuming none of the (numerous) risks pan out
Short term - mania, extreme volatility, chance of major crash(es)

Just to keep some skin in the game, I bought a very small quantity of BTC a while back. I don't care so much if I lose the money in its entirety (we're talking nice dinner with the wife, not bet the ranch), so am somewhat immune to indigestion resulting from 30%+ intra-day fluctuations and all that nonsense.

Would suggest a similar approach to anyone else who is interested in investing in BTC - use your high-risk portion of a balanced investment, and understand that it will fluctuate a lot in value (both directions).