He has more than a twinkle in his eye than usual, and as Ziva notes, he's switched his old-fashioned bow-ties for more modern longitudinal regular ties. I should note here that I've yet to figure out if there is any deeper meaning to DiNozzo and McGee sometimes wearing ties, sometimes not, maybe a more knowledgeable fan can tell me.
But Ducky's switch is definitely significant. He's had a little romance on the show before - he's old but not dead, as I recall Gibbs aptly remarking about Ducky a few seasons ago - but these relationships were always limited, to some extent, by Ducky's needing to take care of his nearly 100-year old mother.
The twist last night is that not only has Ducky's mother died, but Ducky is now also seeing someone. He had a great line about needing some relief from the steady work of dead bodies, and I'm happy for him. Free of ties, familial as well as bow, he's selling his house, buying a brownstone in Georgetown, and can start living his life more to the hilt once again.
5-min podcast review of NCIS
See also NCIS ... NCIS 7.16: Gibbs' Mother-in-Law Dilemma
The Plot to Save Socrates
"a Da Vinci-esque thriller" - New York Daily News
"Sierra Waters is sexy as hell" - curled up with a good book