I've got both garageband and amplitude on my iPhone, as well as various other "payware" apps, and what I realized at the first few purchases I made years ago, when apps were very fresh and new is, "I never use these apps I pay for." As compared to sitting at a desk, and working on a real computer I find these small, handheld devices to be extremely aukward.
Good for gps, good for internet searching and a few mobile websites, great to store contacts, listen to music, keep up with friends, make old school phone calls, write quick and short emails ie not long letters, keep an alarm clock, remind yourself of meetings, jot down quick notes.
Write a dissertation, or produce an album? I still like a desktop/laptop with a larger screen. I simply prefer to type things on a qwerty keyboard, then I do on gorilla glass graphical keyboards, and I prefer a large computer monitor than I do a five-10 inch screen.
Smartphones are a great innovation, and in short order I expect the smartphone to be as powerful as xenon quad cores, with 16 gigs of ram, and plenty of hard disk space, bluetooth to a larger monitor, wireless keyboard and mouse. However that has not happened yet. When it does, than the PC will be dead.
What about this google glass though, what exactly does it do?