Just saw the latest Heinz advert on the tellybox, which uses the classic "You are my sunshine, my only sunshine". Lovely.
Shame it's actually about someone who is heartbroken because their lover left them:
"I'll always love you
and make you happy
If you will only
Say the same
but if you leave me
To have another
You'll regret it all someday
..
You told me once dear
You really loved me
and no one else could come between
but now you've left me and I've got nothing
You have tattered all my dreams!"
Mmm.. Heartbreak and tattered dreams. I fancy some soup. 
What other songs are popularly misunderstood?
Some that spring to mind:
You're Gorgeous by Baby Bird: popular at weddings of a certain era, but actually about being lied to and taken advantage of by someone you love.
Wake Up Boo by Boo Radleys: a summer anthem, that actually starts "Summer's gone"
Barbie Girl by Aqua: cutesy airhead song, that is actually quite cutting about blonde bimbos.
but it's one of those songs that gets used a lot in adverts and happy montages, which always amuses me.
