Since Bitcoin has a hard upper limit in supply which has not been reached yet, its pretty clear that -- barring a major loss in Bitcoins popularity as a currency (which is actually quite probable, and which will counteract this effect) -- its current rate of deflation while its still in the supply-expansion phase is almost certainly <i>less than</i> its long-term expected rate of deflation.
Bitcoin's hard upper limit might make it attractive as an investment, but makes it undesirable as a currency (of course, even with the upper supply limit, the lack of utility value and the fact that bitcoins are essentially intangible make it somewhat dubious long-term value as an investment, but perhaps intangible collectibles will end up as a popular collectors item.)