Save space (and time) with your Time Machine backups:
- Open a Finder window and go to your Mac's Hard Drive
- Open System Preferences > Time Machine, then click Options
- Drag the System folder from your Mac's hard drive into the "Exclude these items from backup" section
- OS X will prompt you to exclude other related items, including system applications. You probably don't need those core items since they come preinstalled in OS X anyway, and your initial and potentially future backups won't take as much time.
Note that you can not do a full bootable restore from Time Machine. But you can still restore all your folders, applications and settings etc. And it will save you about 25GB or more of space!