Folks accustomed to number lock may have a hard time moving from an Apple extended keyboard to the more compact keyboard layout found on Apple's wireless keyboard or its MacBook models. If you can't live without num lock, then you should check out the NumLock app, a Kickstarter-funded app from developer Dennis Vogel.
NumLock runs in the background and provides you with a hotkey combo or menu bar item that'll toggle NumLock on and off. When enabled, NumLock lets you use the 7-8-9, u-i-o, j-k-l and m-,-. keys as a numeric keypad.
Vogel already has a working version of the app and has turned to Kickstarter to help fund some of his early development costs. If he reaches the $574 Kickstarter goal, the app will be released as freeware. You can read more about NumLock on the app's Kickstarter page. The Kickstarter project already has a few backers and will end on Thursday April 4th, 11:47 AM EDT.