I've never confirmed them from home and I never had an issue. When you get to your WDW resort, you can just ask for an ADR print out right at check-in and they'll easily print one out for you. Kind of my way of confirming I guess.
I usually make my adrs at 180 days and call to reconfirm about a week before we leave. I rarely if ever make any changes before we get to WDW. I made no changes for our Dec. trip last year but when I went to confirm I found out I had a booking for a lunch that was never on my plan. This was a first for all of our trips. I cancelled it and so someone else could have it but I would have been livid if it were in reverse and the reservation had never been made. I know mistakes can happen and that's why I would like to know everything is ok before I leave. I'd rather not have a surprise when I walk up to the restuarant unless of course it's for the castle stay.
I am planning to confirm. Just in case I wrote down the wrong time/wrong reservation #. I just like to double check. I will do anything to make sure my vacation runs smoother.