I've been having the same problems plus a few more:
1) Can't actually exit the game when I try to (have to click on red button in upper left corner of screen).
2) Most purple warp zones crash the game.
3) Some levels in Super Meat World crash the game.
4) Lag spikes.
5) Can't make the game full screen and can't change the resolution (though I now know that I can change the resolution and quality in the command line).
6) After I got the first key In the boss fight against CHAD in the Hospital world, the level didn't start scrolling up and I was just stuck with CHAD jumping out of the water. This only happened once but I thought I should mention it.
7) I got the Alien Hominid character but when I'm playing a level and I try to switch characters he doesn't show up. However, when I'm at the world map and I'm asked to select a character before I start a level, he DOES show up.
Also, I've noticed that the more a level gets coated with the red stuff that Meat Boy leaves all over the surfaces and buzz saws he touches, the more the level seems to lag. This even happens for me in an 800x600 window on the lowest quality settings. Exiting out of the level and re-entering into it so that his "secretions" aren't all over the place makes the game run much smoother, at least for me. So I must ask:
Is there any way to turn off the red stuff Meat Boy leaves all over the place to prevent the game from lagging?
15-inch (1440x900) Mid-2007 Macbook Pro (Non-unibody)
Snow Leopard 10.6.8
2.2 GHz Core2Duo
6 GB 667 MHz DDR2 SDRAM
128MB Nvidia GeForce 8600M GT