All depends on what you want to know. I'll give you the details from a user/non-technical perspective.
- Android Market: You hear a lot of talk about the iPhone App Store. Well, Android has one too. And while the App Store may in fact be the gold standard, the Android Market is #2 in app stores. Android has tens of thousands of apps. And before getting brainwashed by Apple fanboys remember: the iPhone has been out for 3 yrs. Android for 1. So it's doing pretty good for such a short period of time.
- notification bar: Save the Palm WebOS (running on the Palm Pre) there is no other phone OS that notifies better than Android. In addition to the regular stuff you'd expect (battery life, time, wi-fi, 3G, etc) you get notifications from other apps. If someone sends you a text, you will see it across the notification bar. You won't even have to open the text if you don't think it's worth reading. It display the first 2 lines or so of the text. If you want to read the whole thing, pull down the *shade*, select the txt and it will open in the application you choose.
- use any app you want: In the case of text messages (or any other app for that matter), you can use any app you like. E.g. there's the built in messaging app, ChompSMS, Handcent and many others. If an app offers to send a txt, every single app that supports sending and receiving texts will be presented to you. You select the one you want. iPhone won't let you do that. If an app duplicates the functionality of an existing iPhone app, you can't install it. In fact, you won't even see it because Apple would have rejected it from the App Store. Android lets you use what works best for you. Don't like the built in music player? Install TuneWiki, MixZing, RockOn or whatever you like. Unlike Apple, Google actually ENCOURAGES developers to expand on what they've already done by including the APIs required to share data (such as your playlist--ok, a *little* techie. I promise, no more :-D )
- multi-tasking: Let's say you're listening to music (from the music player of your choice- built-in, TuneWiki, RockOn Music Player, MixZine Music Player, etc - your choices on the iPhone are the built-in player... that's it). You're also checking email. But you're on the train and need to let someone know when you reach a certain point. Hence you have Locale running in the background using location services. It detects you've made it to a certain area that you choose and sends a txt to the person who needs it. All without ever stopping your music or requiring you to send the txt. And if you leave an app by hitting the home button, you can go back to the first app at the same place it was where you left it.
- lock screen: No longer do you have to remember yet another 4 digit password to get into your phone. Android uses an unlock pattern. Not only is it more secure, it also looks cool to non-Android users.
There's a lot more but I think this should give you an idea why Android is taking off. To get more especially on the technical side (which is actually what sold me on the OS), go to YouTube and search "android architecture".