Boy, a lot has been said here and you will excuse me if I didn´t read all the 27 pages of discussion!
First of all, I voted "against", but mostly beacuse I see no reason to change the reward mechanics from games such as BG, ID, PT, Fallout 1&2, etc. I think they worked perfectly fine, and they´ve been implemented in what many people, including myself, consider to be some of the best games ever made. The possibility to gain experience for every kill never made me play a murdering psychopath, and I´ve never felt like I´m missing on something or that my character is somehow less powerfull just beacuse I didn´t murder that quiet village of fishermen, even though I predominantly play with combat based characters.
I noticed that a lot of you people are worried that excessive metagaming would occur. I say; so what? Again, did any of you think any less of Baldurs Gate 2 just beacuse you had the possibility to kill of an entire city to get that extra exp? Besides, some metagaming will occur with all but the most casual of players, and honestly, imo that is a part of makes RPGs so enjoyable.
Now, having said that, I hope nobody here seriously thinks that this reward system is the only way to go. These are Planescape Torment and Baldurs Gate devs were talking about here people! If anyone in the industry today is capable of creating a new fun and rewarding RPG system, that will make you want to play this game over and over and OVER again, it´s these guys. The last thing that should happen here is to let the devs feel forced to implement a system they dont want, just beacuse of popular demand. The simple truth is that we have no idea what exactly kind of a system they are capable of coming up with. But then again, it would be foolish from the devs to ignore this forum, simply beacuse I think a lot of great ides have been tossed around here, and I hope they will take into consideration what is being said here (and I think they are already doing that).
I see no problem in giving no exp for a goblin, but a considerable amount of exp for an ancient demon trapped in some distant corner of the map. I think the main issue here is how to reward players who take their time and explore every inch of the game world. Will only loot be enough? Consider this; if you are not given any exp for killing a creature for the sake of "not encouraging murderous behavior", then why should you find any loot on them as well? Loot = money = better equipment = more powerfull characters. Your fallen enemies not leaving behind any loot seems a pretty blasphemeus idea for an RPG. If anything, rewarding people with money for killing other people seems more twisted than simply acknowleging they´ve learned something from the process.
Again, players that wan´t to kill everything that moves beacuse it gives them sick pleasure will do that regardless of the rewards.
In the end, after all I´ve read in here, the hybrid system seems to make the most sense. Different types of enemies give different amaounts of exp, ranging from no exp (I see no problem with most creatures in the game world falling under this category) to large amounts of exp.
Killing a pack of koblods at lvl 1 will be a daunting task, but at lvl 15 you wont even notice stepping on them, so no exp for you!