Most the excitement about the press release is due to the vague nature of the press release and the incredibly interesting backgrounds of the researchers who are part of it.
The statement NASA released says:
NASA will hold a news conference at 11 a.m. PST on Thursday, Dec. 2, to discuss an astrobiology finding that will impact the search for evidence of extraterrestrial life
So this is most likely going to be something about conditions on another moon or planet conducive for life. Of course, the speculation is that NASA will announce the discovery for life. Maybe. I can't rule that out, but it seems really unlikely; I don't think they would announce it in this way.
We've put together a slideshow of all the twitter reactions and will be updating this entry as th