I own a
Arduino Leonardo, and I also know someone who has a Raspberry Pi.
The main difference between the two is their applications.
The Arduino is a micro-controller. It's simple board with a tiny CPU and memory bank. This is by no means a computer, it's a tiny device to make electronic projects easier.
The Raspberry Pi is a full blow computer, able to run Linux(full GDM possible).
The Arduino is primary for hobbyists, and the most you'll be able to do on a default board is blink a few LEDs.
What makes the Arduino awesome, is the SDK that comes with it. It's written in kind-of-a C style, and contains libraries for interfacing with pretty much everything you can think of.
The software of the Arduino itself is only a bootloader, along with your instruction set.
As for learning Linux, it's never a waste of time to learn something new. But you'll have to change your attitude on Mac/OSX before you delve into this work.
A long time ago, UNIX was created. A few branches spread out, one of them was NetBSD, which Apple took and adapted to OSX. OSX is pretty much Unix.
Linus(creator of Linux) created his own kernel based vaguely on Unix, but there are some similarities still. Once you overcome the kernel aspects of it, most tools you will use on Linux was originally built for Unix and then ported by GNU to Linux.
here's a link showing a diagram for how Unix envolved:
http://upload.wikimedia.org/wikipedia/c ... simple.svg
But enough of that, you should be asking what flavor of Linux to greet instead of should I be learning Linux.
There are many distributions. As an example to that, there's even Justin Bieber and Hanna Montana distros.
Most beginners start of at Ubuntu, or some port of it. It's not a bad /desktop/ system, but since you're a programmer already I'll suggest you go up in the chain back to Debian.
They're busy releasing version 7(wheezy), which is the first one to come natively with GNOME3(a desktop environment).
Note: This opinion is highly biased, just as most others will be. Please try out a bunch of different flavors and choose one that YOU like the most.
I'm thinking getting a raspberry Pi so i can code mobile 
And raspberry uses linux so.. 1+1=2
