I agree re: places where people don't wait til 6mo etc.
What about HPV? I know it's mainly contracted by genital contact, but what if you have papillomas in your throat or mouth? I had one, was not aware of it til a doctor saw it during check up.
Of course, it's not very likely, but still, it seems quite an unhygenic practice to me.
And, yes, baby might get that cold or flu through everyday contact, but not necessarily, while feeding him your saliva is pretty much guaranteed to make him catch it.