I agree that there are a lot of senseless apps for things like, as you say, calculating tips which should be second nature. Interestingly I recently watched a video regarding the future of "augmented reality" in smartphones. The application used the accelerometer, magnetometer, gps receiver, camera and facial recognition technology to overlay information on the screen when you pointed the camera at people and objects. Here it is....
Now that's pretty cool but it does give us another excuse for not actually talking to people. One of the excellent things I like about the iPhone is it's the first phone I've owned that can reliably merge my desktop and mobile activities. Having email synced (not just the emails themselves but whether I've read them or not) across multiple accounts. Also, traditionally I could only sync my contacts between PC and phone when they were physically connected now they stay synced without my intervention between PC, phone, facebook, Gmail, and any other application I can think of. Yes I know, abilities like this never seem to originate from Apple themselves but they have done a good job of bringing together/plagiarising? lots of ideas into one package to make a really useful product.