What happened to Minecraft?
Is it the new slim model?
In short, it's really bugged now. Most people have had to start entire new maps because of the 'changes', and even then there's still a lot that doesn't work proper. The longer story is much more head-shaking though.
A while back, Jeb (essentially 'the other' programmer) got put on duty for making the Android version so he didn't code anything on the normal releases. Notch took it upon himself to start adding new features without fixing old ones, and it got really backed up. The recent 1.6 release was going to be a bug-fix release, where he actually went to the minecraft-wiki page and fixed everything on the list (100+ items). Then, he added 3 features to the game and released it.
Within 2 hours, he had to release 4 more separate bug patches to fix the new things he just broke. Then another 2 patches over the next couple days. Now, the bug-list is back up over 100 again. Notch has great ideas, but he doesn't know anything about QA apparently. He never knew that the mac-client didnt work well until the first time he used it... a couple days ago.