According to Chris Elliot, one of the bloggers involved. Link.
No word on whether the TSA has also dropped the subpoena issued to the other blogger, Steven Frischling. Both subpoenas have now been dropped, Frischling's too.
Update, Jan 1: Wired has a story here, Associated Press here. One theory: yes, TSA has dropped the subpoenas against the two bloggers, but only because it already got the information it needed from copying data off Frischling's hard drive (more paranoid folk have also suggested that when the hard drive was in the agents' possession, they may additionally have installed keylogger software or similar surveillance apps). The Gmail account information of the leak source, who is reported to be a person employed by the TSA, plus a possible subpoena issued to Google (which has a good track record of protecting user privacy in these cases, but who knows)? That might have been all the feds needed. So this may well be good news for the bloggers, but not for their source.
Speaking as an attorney, I would advise you not to let this go. Make an ethics complaint against the government attorney that signed the subpoena in DC or the jurisdiction they are licensed to practice law in. You don't subpoena someone, then just "let it drop."