This is my first MAC also. I ran across your post while trying to do the same thing. I am surprised at the lack of a totally free tool to perform such a simple and common operation as create an org chart. On my PC I can easily create org charts using Powerpoint or Excel both part of the Office Suite (so kind of free because I have to have them anyway). You can also pay for Visio which is great at creating org charts. There are also some free tools you can download. And of course you can use the basic drawing tools in word pad to laboriously create an org chart.
I found on the MAC that no such tool is free, except for laborious method, which is only kind of free. I found OmniGraffie which looks awesome and I wish I could afford. There is also a tool called Edraw which is shareware. I found uppercase OrgPlus for a 30 day free trial (it says freeware, but that seems like shareware to me).
I did purchase a copy of IWorks when I purchased my MAC Book. I should have paid the extra $70 for Office. Anyway, you can create an orgchart in keynote using boxes and simple lines. It is tedious , but it works.
Let me know if you found a better solution or if some MAC guru out there knows a better solution let us disillusioned folks in on the secret.