I think for me I hate more songs now that I used to love, than vice versa. 

A lot of songs by the group [i]Breaking Benjamin[/i] I can't stand to listen to. Not because of any fault of the songs, but because when I went through my 'angsty-teen' phase I listened to them over, and over, and over again. ([i]Until The End[/i] by them is probably the best example. Though I still love the intro to the song.)

I have a similar issue with [i]Two Steps from Hell[/i]. When I first found them years ago I was so obsessed that now I can't take a lot of their music seriously. Even their newer stuff doesn't jibe well with me. The only song I still love by them is [i]This Must Be The Mothership[/i], but even that's beginning to get old.

My favourite song of all time for a [b]very[/b] long time was [i]To The End[/i] by [i]My Chemical Romance[/i]. I don't hate the song, but for the same reason as the ones above, I just listened to it way too much. I'd still classify it in my Top 50, but that's a huge step down from #1.

The only band I can think of that I used to hate but now love is [i]Panic! At The Disco[/i]. Was always more of a FOB or MCR fanboy growing up, but as of late I'm listening to more P!ATD than either of the other two.