Re: Minecraft running slowly?
You might give some clue what video card and driver you are using. If not sure, post the output of sudo lspci -v related to your video card/chip.
I have generally found minecraft to run faster in Ubuntu than in Win7. Although, that is most apparent when testing it on AMD C-50 1 GHz 2 core 2 GB tablet PC w/ATI HD graphics 32-bit Win7 Pro vs. 64-bit Ubuntu 11.10 (openjdk-6-jre) where it is actually playable in Linux and not so much in Windows.
I did have something strange happen on my desktop. It has generally been running 150-250 fps and I thought 12w26a snapshot was running slightly faster. But suddenly Sunday in 64-bit 11.10 it was running 25-30 fps (smoothly with no lag) even in different worlds or when game restarted, and my video card was more than 20 degrees C cooler than normal. I copied .minecraft dir over to 12.04, booted that, and that was back up to normal speed. I booted back into 11.10 and then that ran normal speed. So I don't know why minecraft was temporarily running about 10% of its normal speed even though gpu and a core of cpu were full speed (but gpu much cooler).
It ran full speed in 64-bit 10.10 too, but I recently replaced that with 12.04.
i5 650 3.2 GHz, 8 GB, nvidia GTX 1060, 32" 1080p & assorted older computers