I can't really speak for BB10, but as it stands now on OS7 if you are on any screen other than the homescreen then yes, the notifier is the LED. On the homescreen you get a notification icon in the notification bar (soon to become blackberry hub) and a notifier on the text/email/whatever icon that the message is in. You can definitely set different tones/music for different contacts, different types of message, whatever. In OS7 you can (via an app called BeBuzz) set the LED to whatever colours or combination of colours you want for different message types or contacts, so for most of us in crackberry nation the LED alone will tell you who sent you a message or at least what type of message it was (I have green for general email, white for work email, blue for BBM, purple for texts, pink for my girlfriend, yellow for my boss, turquoise for IMs). Also within BeBuzz you can set it up to give you 'toasts'; a pop-up that gives you the top few lines of the message along with the sender ID. Some people like it, I don't, it feels more invasive to me.
Originally Posted by bobo616
With BB10, we can reasonably safely assume that certain things will stay the same. No on-screen notification of messages unless you are looking at the icon for the appropriate message box (or BBHub, I'm not sure if there will be separate inbox icons anymore but I suspect there will be). The LED is there to tell you you have a message, and I suspect we'll either get the colour changey goodness baked into the OS, or with BeBuzz. You also get the vibrate and whatever tone you've set. From there you swipe up to get the notifications bar to pop out from the left which will have icons for messages in it telling you what is unread. Then you swipe left to peek into the Hub and see the message. It will take some getting used to.
One of the big things about getting used to blackberries is getting used to the LED doing all kinds of work, and its the thing everyone misses too. The concept is that you have put your BB down and on silent, but still have a visual cue there for important things. In meetings thats a pretty big deal; you have your BB on the table and can tell at a glance if you need to duck out to take a call or not. Also, believe it or not, the LED is part of a package of things that save battery life. On any device, having the screen light up is the biggest battery drainer but a BB's screen won't light up unless you tell it to.