What is Wrong with Minecraft?

It seems like something is completely broken in Minecraft nowadays. Whilst playing my 1.5.2 game, I realized that monsters have stopped spawning in the Overworld. I noticed this several days after installing the newest backports of Extrabiomes XL and Plunder Rummage. I spent a couple of days mostly in Atum and Twilight Forest, and upon my return I noticed the centaurs around my home were suspiciously absent.

Checking the F3 screen, there were way less entities than normal, and enabling the radar option of Rei's Minimap confirmed a severe lack of hostile mobs. I immediately checked the usual suspects - difficulty setting (Normal, as it's been since the beginning), config files (nothing wrong), gamerules (all in order). My Forge log showed that JAS wasn't spawning anything in the monster category... but monsters placed in other categories (Mo' Creatures rats in the "underground" category) spawned correctly. This issue happens regardless of spawn system (vanilla's or a mod's), anything in the "monster" category simply does not spawn.

I then thought that perhaps one of the backports had caused an issue, so I reverted to previous versions... with no success in getting monsters back. I posted my problem on the EBXL and JAS threads in hopes of resolution. The mod authors are still scratching their heads.

After some testing, I found that logging out and back in will cause monsters to spawn for a short time (perhaps a minute at most). Forge then spits out a "Something's taking too long!" error that mentions 'root', but doesn't say of what. I took that as a sign of a possible corruption/error, and rebuilt my minecraft.jar, reinstalled Forge and LWJGL... it didn't help.

Odder still, this issue is only happening in the Overworld. The End, Nether, Atum, and Twilight Forest work perfectly fine. I haven't made any Mystcraft ages yet, so I've no idea if they're affected.

I've been given some advice and a DEV version of JAS that includes more debug information, so perhaps I'll resolve this mess. My biggest concern is that I won't find any issues, then a month down the road it will reappear, putting me back to where I am now. My build was stable for about a month, then this happened. What's to say a series of test runs of only a day or so will be enough to replicate the error?

So, while I was waiting to hear back from the mod authors, I figured it was high time I finished the race track map for 1.6.2. I was able to copy the save over from 1.5.2 into the 1.6.2 launcher and get Forge, Optifine, and Rei's Minimap installed, so I could at least get that accomplished.

I was building the hotel when I started getting horrendous lag. I've read up on memory settings, and have done everything I know of to eke out the best performance I can. Even with 50 mods, 1.5.2 only lags when generating new areas... so how would 1.6.2 with only 2 mods cause this? I've been reading from the forums that Forge made some rendering changes in 1.6, and it's causing issues with Optifine. As far as I know though, there's been no official announcement and no hard data to back up the claims of incompatibility. Still, there's a lot to be said of the user experience, and if people are saying there's an improvement without Optifine, it's at least worth giving it a try.

While I'm here, I should mention that Mojang recently mentioned the upcoming additions in 1.7. Yes, you read that correctly, 1.7 development is well underway, and we'll be seeing snapshots for it in the near future. Current features include new biomes and reworked terrain generation (no more taigas next to deserts, apparently). While that's all well and good, the modding community is already drowning in bugs and incompatibilities from 1.6. The major modpacks are still sitting in 1.5.2 because of it, and 1.7 is just around the corner? Really?!?

Also, take a moment to realize what 1.7 will be changing... terrain generation. Good luck to the authors that write ore, structure, or biome-adding mods - it seems your time has come to get the shaft. I hate to spout "doom and gloom", but if changing the launcher and adding horses and some new building blocks caused this much trouble, what will rewriting the terrain generation code do? I shudder to think...

All I know is that I haven't been able to keep a game world through various updates past 1.4.7 due to mods not updating mainly due to new bugs/incompatibilities. Now, I can't even get some of the basic elements of the game (monster spawns and decent framerate) to work right. What the heck is going on here?!? At this rate, I wouldn't be surprised if starting up 1.7 just gives you a blue screen of death.