Given that (at least for now) you're in it for fun, and that you already have Mac hardware, seems to me iOS is a good place to start. With the combination of the iPhone simulator and your iPod Touch you have what you'll need to dive in.<p>One thing other posters haven't brought up is the abysmal condition of the Android emulator. Unless you have an Android device on hand, you're in for a world of pain trying to develop apps using the emulator. It's snail slow, with a long boot-up time & very poor graphics performance. (It's something the Android dev tools team at Google is working hard on fixing, but it's a ways out, from my understanding.)<p>Finally, if you're the type who likes a structured approach to learning there's a great course that Stanford University offers covering introductory iOS development (<a href="http://goo.gl/SouE" rel="nofollow">http://goo.gl/SouE</a>) to help get you started.<p>Good luck to you, my friend!