Just picked up the game off steam last night, pretty much the same problems as everyone else:

Mac Mini
Snow Leopard 10.6.8
GMA 950 graphics *fear the power -- it sucks so hard it'll rip your face off*
2 GB ram
1.83 Ghz Core 2 Duo

1) Game crashes attempting to enter any warp
2) Exit Game menu from the Main menu is useless
3) Can't enter full screen or change resolution
4) C.H.A.D. level gets stuck (frequently) on first key (able to pick up key to blow up wall/chain thing but won't trigger the scroll until i go back to where the key was)  2nd key the scroll position jumps up then back down, kinda annoying/disorienting, 3rd/4th keys i don't get the  "filtered light" effect as the roof blows ... probably just a shortcut/graphics limitation but whatever -- i noticed.
5) Unlocked "I have crabs" achievement game crashed (some kind of warp it seemed)
6) Level 4-20 (heh) Babylon - Frequent "spontaneous" deaths while riding first moving platform.  Seems to occur after i have died on the level ... if you just throw yourself into a batch of spikes (or lava?) in the first section, die (obviously) and then revive you will start to die by just getting on to the platform -- not touching anything which would cause death. Might take 4 or 5 times for it to start happening.
7) Character selection screen (the one when entering a level for the first time, NOT the switch-character screen), can't ESC out back to map (grr), the bandage numbers displayed on each character "ghost" image are a bit hard to read (font seems scaled wrong and/or top and bottom clipped )
8) In Super Meat World area (not the world-map selection, after that), no keyboard input works (meh), "system" mouse cursor is not hidden and covers "game" mouse cursor.
9) Super Meat World, "LEVELS" screen. Game crashes after selecting a level from the "recommended" list (picked several at random, one was titled "relax"). Also crashes from "chapters" list (picked another couple at random, one titled "the rackets").  Had more luck selecting from "levels" list "Level of Dooooooo" crashed "Rocksalt.pcx" also crashed others seemed to load okay ... it probably has more to do with what the contents of the level are rather than where you select it from but .. well ... that's for you to figure out i guess ;-)  
10) Super Meat World, having to click the actual arrow for "previous" and "next" rather than just clicking on the arrow+word area is kind of annoying.
11) No idea what the key is to save replay (can't make out the graphic) ... kinda pressed all the keys on the keyboard, nothing saved anything.
12) Sound/Music volumes are not saved between sessions.
13) Able to die from Dr. Fetus' missiles well after they've exploded on a wall even on -ultralowdetail mode. (some kind of lag? game overall was running smoothly except on -highdetail).

will undoubtedly run into more -- will update as i run into them.