In the notifications settings/preferences, on a per-app basis, you can set whether notifications are displayed to allow banners, badges, and sounds. And you can turn on/off whether the notification posts to the lock screen, or stay in the notification center (swipe down on iOS, click the clock in the menu bar on OSX)
I'll have to look into this, but my experience has been that Notification Center: doesn't display everything; loses things on a whim; gives no way of recovering things, or displaying all things.
It definitely does. One reliable way I've noticed for this to happen is if you have the app that caused the notification open on another device. Presumably that app is then saying to the notifications system "don't worry, I've got this", but then that notification disappears on all devices.
Last year I made a wine cataloging app for iOS based personal gripes that I had with all the others out there. I just wanted something incredibly simple, and all the others were ugly and complicated.
I was inspired by the 7 minute workout app posted here, and set aside 8 hours to build the whole thing. All told I ended up spending about 40 hours on it and haven't really touched it since.
I started selling it at $.99, but sales were slow and I wasn't really making anything at all off it. So I raised the price 5x to $4.99 and sales didn't really change much. Now it brings me in about $50-150 / month that I use as extra cash toward paying off my student loans.
