They're all "real". Somebody, somewhere, traded that tick, fiat (or gox$) and bitcoin changed hands. If you consider the 4 largest exchanges (together about 90

They're all "real". Somebody, somewhere, traded that tick, fiat (or gox$) and bitcoin changed hands. If you consider the 4 largest exchanges (together about 90% of the volume), then you can look at the price as this fuzzy zone somewhere between the highest and lowest tick. If you want to know when a specific price has been surprassed comprehensively, it's when all of the top exchanges have gone over it (not just one). But if you want to know if it's somewhat likely a specific price will be surpassed by all exchanges, then just one going over carries a lot of meaning.