I just recently purchased a new Honda Accord and I have always change my oil every three months whether I needed it or not just as a good habit. I am told by the dealer this is not necessary and that I can now go up to 12,000 miles is this correct? Has anyone had this experience?

I would use 5W-20 full-synthetic engine oil (e.g. Mobil 1) and change it, along with a premium filter (e.g, Purolator's PureOne), every 6,000 miles or 6 months, whichever comes first.