From what I've learned of recent discoveries, an "RNA world"(since RNA can both carry information and catalyze reactions) under early Earth conditions is almost inevitable, and it seems a DNA world would eventually ensue via natural selection.
Life didn't get much further than that for a couple billions of years, when eucaryotic life appeared, and then again for a couple billions more for multicellular life to appear, and since then it seems to have taken its own sweet time evolving into sentience let alone consciousness. Indeed, it took major extinction events to shove things along. These events therefore seem perhaps to be rare and highly unlikely steps -- steps that may make us close to unique.
Since we don't know how often worlds like the what the Earth was when life first appeared might be (mass, temperature, tectonic activity, oceans) we cannot even assume the most primitive life will be common, but that does seem likely. Other than that the signs are that the evolution of a technological society that survives for any length of time is going to be really rare.
Of course we only have our own history to go by, and we may have been real slow-pokes and these things may happen more often than what our history might indicate.
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