NT replies: it just means there is no news worth telling anyone about...nothing new or exciting worth talking about has happened. it means, "same old, same old."
for example, if 2 weeks have passed since i have spoken to my sister, she'll ask "what's new?" and i could say, "nothing to write home about" meaning nothing is new or exciting since we last spoke.
if a PERSON is nothing to write home about, it means that there is nothing serious happening with that person.
example: let's say i meet someone and have a few dates but it's going nowhere. then it's nothing to write home about...meaning, we won't be falling in love, getting married, etc...
"home" implies telling friends or family about the new relationship... it literally means one does not need to share any details of the other person with their friends or family because the relationship isn't important enough to bother discussing.
i hope someone didn't say that about YOU and i hope you didn't get your feelings hurt.