I've seen a bunch of people in the past few days say things like "Well, the Large Hadron Collider has started up, and the world hasn't ended, so the fears about it were groundless."
On the one hand, as far as I can tell, the scientific community's consensus is that the LHC poses no threat. And I'm happy to believe that. In other words, I agree that the fears appear to be groundless.
But the folks who've said that the threat has been disproven experimentally by the LHC being turned on are a little premature. The first beam was fired this past week, but the first collisions won't be happening for another 6-8 weeks (according to Wikipedia's test timeline), and it won't be operating at full power until sometime in 2009.
So it may be a good idea to keep an eye on the Has the Large Hadron Collider destroyed the world yet? web page. It will tell you at a glance, at any given moment, whether the LHC has in fact destroyed the world. If you don't want to have to keep checking that page, you can subscribe to the site's feed so any change of status will show up in your feed-reader.
I think we can rely on this service. The person who put it together is so confident in its accuracy that he offers a guarantee (viewable in the page's source code):
if the lhc actually destroys the earth & this page isn't yet updated please email [address redacted by Jed] to receive a full refund