I've never really had this experience.Before I had players that would go out of their way to force more fights for xp, that never let anything live if they could help it, and now.... if they butcher a bunch of npcs, it is because they are annoyed or bored, not because they are being rewarded at a system level.
If players are forcing fights to earn XP, which - but for the XP system - they wouldn't be engaging in, doesn't that just show that something is wrong with the system? That is is not driving play in the way that people want to play the game?
I agree with [MENTION=93631]Greg Benage[/MENTION] - "milestone" is about pacing, and that does not particularly depend upon AP vs other campaign styles.I Find milestone is more about what you are going to encounter and works well when running adventure paths or linear campaigns but xp is more about what your characters have experienced and i prefer it when I run sandbox
At the moment I am running two 4e games - in one I have awarded XP per the 4e rules, in the other I'm not bothering and we'll level the PCs when we feel like it. In practice I don't think there will be much difference, as the 4e XP system is basically a pacing device anyway - you get an encounter's worth of XP for every hour or so of play (be that via XP award for combat encounters, for skill challenges, or for free roleplaying), and so it's seems sensible enough to do away with the intermediary device and just award the levels based on pacing considerations.
As a DM, the now-known-as-Milestone-Advancement always fell...cheap?
If the XP system is basically "You get XP for doing these things which you would be doing anyway, because they constitute playing the game", then I don't think milestones is any cheaper or lazier.Mile stones are, for me, a lazy way to level and it also have the pernicious effect of encourage the 5mwd.
If XP is actually a reward for skilled play that you can't get just by trying, then XP makes more sense. But I don't think that's the main way that D&D is played these days.
The idea that XP should be used to motivate a certain sort of player engagement with the game I don't really get, for the same reasons that [MENTION=6801228]Chaosmancer[/MENTION] has stated - if people are turning up but don't really want to engage with the game, they're already suffering! Why make them have smaller numbers on their sheet too?