Yeah, an app sounds nice, but I'm afraid I won't keep it updated. I have a couple notebooks I use--one is the "official" family notebook, taken from Organized Christmas. It has recipes, decorating ideas, calendar pages for tracking events, and so on. Then I have my hidden Christmas notebook, which is skinny and fits quietly in my purse. I have a page for each family member, where I write down gift ideas and check off what I've gotten.
For anyone who might be interested, organizedchristmas.com starts 10/31. She sends an e-mail a day, to keep you on track so your last couple weeks aren't a mad dash of wrapping, baking, and decorating. I find it very helpful.