Mac OSX 10.10 how to recover data
If you are still using the same computer, your chances of recovery go down with each minute of operation - recovering deleted files is time-consuming, recovering over-written files is impossible. And your computer is constantly writing things to disk.

Restart the deleted machine in target disk mode and connect it to another mac. Get a copy of Data Rescue 3 and use it in deleted-files mode. You will also need alternate storage equal to the original drive size.

After it's done recovering things you get to rename everything. The filenames are gone (overwritten) at the time of deletion, your stuff will be recovered with sequential names (Image001.jpg, Image002.jpg etc.)

And I don't think we have to do the usual lecture on backups. Point is well made?