I've noticed this for a while now... I used to be able to get from level 0 to 30 in my mob farm by watching the entity count get to around 150-160. I understand there were changes to the XP system, however throughout the snapshots, and now in 1.8 itself, I've found that I barely get to level 30 with 150 entities. I thought this might have been a diminishing rate of return, but when I manually kill maybe 5 more, I easily get to the next level. ** This is a skeleton farm and I soften mobs and then splash a heal potion on them for the kill.

This evening I let it get to 192 and I got exactly level 30, which seems to be not so much a diminishing return as it is something wrong with the XP algorithm.

I AFK'd and forgot about it, and came back to 311 entities in my farm. After killing them all, I ended up with level 31. I manually killed about 10 more and ended up with level 32 or 33.

150+ entities should get you more of a difference than 1 or 2 levels! Can this please be looked into? XP farms have been nerfed, I get that, but this isn't right.