Wow.
I've been um-ing and ah-ing over posting pretty much this same question, but held off because I knew the majority of answers would be "If you can make it work, then go for it."
My situation is this - main character is written in first person, a secondary character is written in third person. The majority of chapters are the main character, with sparodic chapters from the secondary. It doesn't bother me, but I am the fool writing it, so my opinion doesn't really count, in a sense.
The only time I've come across this was James Patterson's When the Wind Blows. It was a novelty when I began the book but just blended in as I went along. And it was certainly easier on the old noggin than The Time Traveller's Wife, where both main characters are in first person. (btw, loved this book, but it was still a little iffy at times regarding who's first person you were with.)
I know I've personally done the right thing by this story, using first and third person. All can I hope is that the story itself is good enough.
Cheers, Lisa.