That was not just a friendly little peck. They had romantic feels for each other. In Superman #5 Superman has a romantic dream about Wonder Woman.
He thinks to himself "Wow! That was intense! I've had dreams before, but never one that tapped into so deeply into my innermost feelings! And I can't deny it. Wonder Woman has been on my mind a lot. Amazing! Over the years I've more or less contented myself with the fact that there's no real place for romance in Superman's life. Apparently my subconscious mind this otherwise. And it could be right. Wonder Woman would seem a perfect match for Superman."
In Superman #7 Clark tries to get in touch with Wonder Woman by calling the Boston Globe. He thinks to himself, "I feel like a schoolboy calling the prom queen for a date! Am I acting crazy or what? I can't seem to get her out of my thoughts."
In Wonder Woman #8 Julia Kapatelis writes in her journal, "Most interesting is the strange silence that would come over Diana whenever I mentioned Superman. She would not talk about him -- as if some unspoken secret existed between them."
In Wonder Woman #16 Diana walks into Vanessa's room, Julia Kapatelis's daughter, sees the new Superman poster Julia had just gotten and says, "Vanessa, I've seen how you feel about Barry--! Perhaps you are the only one I can speak to about this...In my dreams he is so like a God."
Vanessa says, "You're kidding!?! You mean you've got the hots for Superman?!?"
Diana says, "I am merely saying I cannot explain the feeling that comes over me when I think of him..."
Vanessa says, "Diana, that's great! It means you're in love!! I mean, Superman is perfect for you! So when are you going to tell him--? I mean if Superman feels the same way?"
So Wonder Woman's publicist Myndi Mayer calls Clark Kent at the Daily Planet and Kent says he's geting his friend Superman on the phone and he and Diana arrange a date for the weekend.
In Action Comics #600 they meet and kiss and hold hands and fly together. I'd say they were romantically involved.