I'm glad Melissa and Lisa jumped into this thread, too, because "how much is too much" is something that changes, definitely, the more books you have out. First of all, I think people love seeing authors excited about their first books. Every little step that new book takes into the world is thrilling — every page proof, cover reveal, ARC, early blog review, pro review, display at your local indie, first copy spotted at Barnes and Noble, someone reading it on the subway, etc etc etc — they're all thrilling. And I think for new authors, readers love to hear about that bubbling enthusiasm. They utterly believe that it is just that exciting to have your first book or two out. AND IT IS!
So I think it's difficult to overshare as a debut or second book. So long as it is sharing and not promotional, I think people will laugh and enjoy your giddiness.
I do think, though, that it changes with the more books you have out. Not only do I, as an author, feel differently about my books coming out now than I did as a debut, but people would view my enthusiasm differently, I think. I remember when I used to post every new cover and starred review here on the board, and it never, ever felt weird. Now, though, I think it would feel weird. More . . . gloaty? Even though I haven't changed — just my career has.
This is really not to say that I'm not excited out of my mind about The Raven Boys coming out in two weeks. But the things that I'm thinking about it now are not easily bloggable. They are more nuanced, and a lot of times, more secretive too. As everyone here with a contract will know, the more books you have on the table, the more likely good news is something that has to be held for six or eight or twelve months. Which means by the time you're able to talk about it, genuine giddiness is gone.
This is a long reply to basically say BE EXCITED! EVERYONE WANTS TO SEE EXCITED!