Wow! You all have some great ideas. But after reading "Sometimes" by Skfolc, there is no way I could reuse the same song, under the similar circumstances in my fic. She did a great job and now I've gotta use something different.
I agree that Clark might do something mushy-like, indicative of his feelings for Lois, while Lois might do something to reassert her independence. But maybe they won't be able to pick out their own songs, and will be stuck with another's choices for them...just a thought!
Keep those ideas coming, they're really helping me formulate my story.