My long term outlook will change if BTC stays under $4 for a month. This would, in my opinion, signify that bitcoin's long term adoption rate has weakened substantially.
Still, this will not mean BTC won't be worth $100 or $1000 or more in 10 years.
And if BTC stays above $5 for the rest of the year this will not mean bitcoin will not ultimately fail.
+1
This is pretty much what I think as well. With the current fundamentals (namely the size of the economy), I find a stable price below $5 very unlikely and if that were to happen it would signify bad things in my mind. A price below $4 for a month would make me a doomsday-bear.

So far the market has shown very strong bullish signs at below $5 and fairly bullish at below $5.5, at $6 the interest for buying seems to have died. This is where we're at, what happens next is interesting. I speculated on what could happen in the "$/BTC Time Series Analysis" thread.