It makes me happier and definitely more likely to use the site as it makes me feel like my contribution is valued. However, I don't really count number of likes. I wanted to say that "I never pay attention to the number of likes, but maybe I will like zing when one crosses 5", but then I looked at my profile and recent one got 8 likes.
So normally I don't pay attention at all to the exact numbers, but most certainly subconsciously - and frequently half-annoyedly - I see the notifications pile up, and I suppose that makes me both happier and more likely to contribute. However, since I don't pay attention to the numbers, the specific number, 5 or not, makes no difference to me.