Wow, you already got yours?!?! Excellent. I am a Mac user with a Sony Reader as well--I look forward to the Kindle so that I can avoid the hassle of having to open a program for my computer to see the Reader.
I haven't got my kindle delivered yet, but I did try the "...@free.kindle.com and it didn't show up in my "Media Library" online. The files I sent thru my .."kindle.com" addy showed up tho, so for me, the freebie part hasn't worked yet.
I do have several books lined up so that when I open the box, I can start downloading and reading right away.
When you DO hook the Kindle to your mac via USB, does it show up on the desktop?