Never give your characters placeholder names. I was having a horrible time coming up with names for my characters in Mysterious Other Novel and it was getting in the way of my writing progress, so I finally just gave them silly placeholder names. Now that I'm revising, I have three inappropriately named characters whose whole personalities have been built up around the silly names that they're not allowed to keep. This is giving me many headaches. I know, whatever names I settle on will never feel like their real names. I'll always think of them and see them by their stupid, stupid placeholder names. Darn me.
So, just don't do it. Turns out it's harder to change a character's name down the road than it is to come up with a good one in the first place. Learn from my mistakes. Or don't. If you dare.
Has this ever been a problem for you? How do you know when a character's name is the right one? Are there any you've been especially proud of?