there are other lil tricks as well m8.
like right clicking eq8 and selecting the high quality mode.
This is idd a big one, many people do not know there are several settings turned down in Ableton by default...
Going through all instruments and effects and right clicking them to check for some quality setting would be a good idea, the exception might be the reverb which has the quality drop down on the actual interface...
when you have changed it: dont forget to save it as default preset so it will persist!
also in the settings menu you have a tab "audio". On that tab theres an option "Default SR & Pitch Conversion" which is set at normal by default, clicking it will set it to high quality. (SR = Sample Rate btw)
As for the main question, if you really go search on the audiophile and mastering forums, most people will say it is all a bunch of crap...
The main reason why people say ableton sounds crap is because it is so easy to use, therefore more newbs use it who dont know what they are doing (yet)...
In the end its all about the quality of you samples, instruments and VSTs, the rendering in ableton is not distinguishable from any other major DAW...
personally I find when I use Guitar Rig for example instead of the ableton effects, it sound much and much better....