If I had global adoption tomorrow, I'd have no reason to ever sell my coins, I could just spend them as-is without having to worry about exchange rates and fees.

edit: To a certain extent I already can. I've been paying for web hosting with BTC for a couple years now, I can buy electronics and certain other miscellaneous items on Overstock, and there are plenty of other places online (sadly, no local brick-and-mortar) where I can spend them. I'd think with global adoption, though, the value (in terms of buying power, or USD/Euro price, or however else you want to measure it) would be a lot more stable.