we have decided to have both our kids immunised, on schedule and have (i feel) made well informed decisions. we weighed up both sides and decided that immunisation was the way to go for us. I know some people who chose to wait until their kids were 12months figuring that their immune system was better able to cope by that age.
I will add that it is not solely immunisations that have eradicated a lot of these diseases but can also be highly attributed to better hygiene practices and cleaner living, better diet etc - the decrease of these diseases coincide with all these factors.