So following an NPR piece there's a lot of rumour going round about the possibility that Curiosity has found some organic molecules (Boing Boing, Emily's always excellent Planetary Society blog). If this is indeed the case, then it's interesting but not in itself epoch making. To some extent, since Viking, the surprise had been that there have not been organic materials detected.
As discussed in this post, thousands of tonnes of organic material arrive at the surface of Mars every year. Once it gets there, it either has to be got rid of or it accumulates. Recent work has also shown that most of the Martian meteorites studied have been found to contain organics that were aparently created on Mars through means that have no link to biology (Science paper here). So not only should people presume there are at least some organics on Mars -- people have actually found and studied organics from Mars.
Investigations by Viking and Phoenix did not detect organics, but that is consistent both with processes in the soil destroying them and the protocols used to look for them them being unable to succeed due to the presence of perchlorate (JGR paper here). Curiosity's SAM (Sample Analysis at Mars) instrument suite can look at samples in a wider variety of ways (the sealed cups with chemical solvents may be the key) and is looking at somewhat different environments so if they are there it might well see them.
If that's what's happened its definitely interesting, and I'm sure there will be stuff to be learned from the nature of the organics (for instance, saying if they are made-in-Mars like those in the meteorites or whether they got there from elsewhere). It would be a signal accomplishment. But in the absence of organic molecules that look suspiciously lifelike it would say nothing in itself about the likelihood of life. We don't assume that organics on meteorites mean that the asteroid belt is teeming with life. And it woud hardly be surprising. I certainly don't think it would be historic to discover that a surface on to which organic molecules ceaselessly fall has organic molecules on it.
If you don't believe me, here's someone who actually knows:
What’s the likelihood of finding organics? John Grunsfeld, head of NASA’s Science Mission Directorate, said he likes Curiosity’s chances. “If I had to predict the future, I would say it’s likely."