There's a bunch of talk going on here about it:
http://www.ableton.com/forum/viewtopic.php?t=65455
That started as just my issues with the new universal automapping.
But overall, I've always liked the unit. My problem with it is that there are a couple little things stopping it from being the perfect controller. But no controller is perfect, so this is still one of the best.
It's basically broken down into 3 parts for any DAW: Mixer Automap, Plug-in Automap, and manual templates. For Ableton however, instead of mixer automap, you use Ableton automap. Essentially the same idea, but specific to ableton.
-Mixer/Ableton automap (templates 39/40) is to control a DAW's internal instruments/effects and mixer controls. It also has the old way of controlling VSTs/AUs, which is different for every host.
-Plug-in Automap (template 38 ) is the new way to control Plug-ins, which requires the plug-in to wrapped in to a automap version which you must load instead of the regular plug. Then you have control of that plug-in with all of the SL's controls. Much like a template, except you always get three full pages of control, and as many as you want, and you can change devices you are controlling from the SL quickly. The cool thing here, is that you can alter the automap layout to your liking, and have it permanently recall that way when you load it, or save different versions.
-Manual templates (1-36) are much like any other controller. You set any one to any CC you want and do midi learns or whatever. The thing is, the LCD is huge bonus. Even if you didn't have any automapping whatsoever, you still have 36 templates to use how you like, and can name any control.
So in general, with ableton, if you were using mainly internal devices, you'd be using template 40 (ableton automap), and select a device you want to control with the mouse or arrows, and use the encoders for that automapping, and sliders for mixer/pans/sends, and of course you probably want to use manual templates for extra midi learn knobs, because the automap template only gives you the 8 bottom ones. When you use third-party devices, and want a lot of control, then you'd turn to tamplate 38 (plug-in automap) and use the wrapped plug-ins, giving you all controls for the plug-in. If you have more than one wrapped plug-in loaded, it controls which ever one is visible usually, but you can switch control from the SL easily. You just switch between templates whenever you want, going from mixer/ableton to plug-ins.
What I tend to do is use the ableton automap's bottom 8 knobs for an instruments internal midi-learn (as opposed to abletons midi-learn), so that it gets controlled whenever record is enabled for that track. That way, you get those 8 knobs to use for every channel. For example if it's something like reaktor, which doesn't send the names of parameters (so it's not good for plug-in automap), and you want to quickly use the instruments midi-learn, then those bottom 8 are good. Otherwise, abletons midi learn takes up the knob at all times. Might as well use a manual template for that.
Tip for quick switching of templates: Assign one button in ableton's automap to template 38 (plug-in automap) and one to a manual template you want to use (like template 1). That way you can recall it quickly with one press, and go back to ableton with a quick turn to the right of the template knob.
Good thing i just got up at 6 am with nothing to do but drink my coffee and type away.