What will happen if I have to reinstall or if my hard drive has problems?
Apple offers the Lion OSX 10.7 operating system upgrade for sale by download, but no longer sells it on DVD.
If you have installed Lion on your machine, you can make a bootable backup of the installed on a DVD or on a USB memory stick
The easiest way is probably to use Lion DiskMaker software http://www.macupdate.com/app/mac/39701/lion-diskmaker
Or you can do it manually following these instructions http://osxdaily.com/2011/07/08/make-a-bootable-mac-os-x-10-7-lion-installer-from-a-usb-flash-drive/
Keep in mind that this is only for people who have purchased the downloadable installer from Apple because it requires the installer files.
Of course, for any Mac owner, you should have a backup hard drive to back up your data files to, either with TimeMachine or with a backup utility like SuperDuper. You can create a bootable external hard drive by cloning your existing drive with SuperDuper or Carbon Copy Cloner.