Must I reformat my hard drive to reclaim space from unused 2nd partition? I wanted to see if I could also have Ubuntu on my Macbook alongside the usual OSX. Now, a year later, I want to remove the Ubuntu and the space associated with it on the hard drive. That is, my hd is partitioned into two separate spaces. 

My question is, if I want back the space that Ubuntu took, must I reformat and delete everything on my Mac?
You won't need that, you can delete your Ubuntu partition and expand the current OSX one. 

Using Disk Utility :


Choose your hard drive
Under the Partition tab
Delete your ubuntu partition and expand the OS partition.