There is much, much, more merchant acceptance, transaction volume, etc. for Bitcoin compared to the last time there was a big rise; not to mention production is only half of what it was before; ASICs are here/on the horizon, YC has funded a bitcoin startup, it's mentioned basically daily in the blogs of major publications, etc.

It is also worth taking a look at a log-scale chart to see that the rise isn't quite so steep as before: http://www.bitcoincharts.com/charts/mtgoxUSD#tgSzm1g10zm2g25...

Clearly a lot of speculation going on here; but I very strongly doubt we will see a crash anything like we saw last time (how many people were preaching that the end of bitcoin had come?); though a significant correction when people start taking their profit seems almost inevitable.

Anecdotally, a number of people I have been telling to buy bitcoins for years now are finally like, "well okay, I am just going to wait till it drops to $xx or so (where xx is ~40% less than whatever it is at the moment we have the conversation).