Value? None. Bitcoins are entirely fiat, so for every coin that is lost, the exchange rate should compensate to reflect the new supply. It only really starts to become a problem when 1 Satoshi (smallest subdivisible unit) represents more value than we'd like. At the minute the exchange rate is Satoshi = USD $0.0000145925, so there's a few orders of magnitude headroom there.

I agree though that Bitcoin is not a viable mainstream currency.