Around 75 tries, 2 realmom kills!
I've also got a shot of my Isaac (actually Cain, because he's such a BAMF) right before my 2nd kill:

Finding both a dollar and a skeleton key was a godsend.

BRIMSTONE BOY GET!

Took me a while, and a really weird level path:
6-7, 15, 18-20, 5, 10, 12, 14, 16, 1-4, 8-9, 11, 13, 17

I actually had to stop for a while to beat my controller into a wall when I messed up on 11, which is basically impossible to fail with Captain Viridian, by getting distracted and flipping into the abyss. But I did it in the end.

http://steamcommunity.com/id/nephewjack/stats/SuperMeatBoy/?tab=achievements

Just got Golden God after finishing XOXOXO. I still don't have Living in the Past because Steam is being stupid, and I still need to finish Dark Cotton Alley and Dark Dr. Fetus.

I've currently only achieved Wood Boy and Salt Boy, the latter after around 2 hours of pain. I'm probably going to try Squirrel Boy next, if I can get over my frustration.

EDIT: Got frustrated with Squirrel Boy, so I achieved Needle Boy.

EDIT2: Recently got Dead Boy with little trouble, and Blood Clot Boy with a huge amount of it. I ended up doing 11-12, 1,8, 16, then breaking most of the rest of them with Viridian/the Kid.

EDIT3: Squirrel Boy Get!
Also, this topic is dead, dead, dead.