hi guys. I'm Sylvain who solved the thing, thanks for relaying the info here! :)
The blog indeed crashed, it's on a very small VM with a remote filesystem and even with a WP cache plugin.. not so much luck, even with apache stopped.
However our company blog has a proper sysadmin ;-) So after I setup a redirect there no more issues... until we get on slashdot maybe ? :)
Cheers!