I had to carry one of these out of the middle of a freeway last year.
The three toes are fine to carry, but the two toes are a little quicker, and they'll scratch the shit out of you.

That poor little fella looks like he was about to fall asleep for half the trip.

"Is that a car coming?"
"..."
"Nope."
"..."
*moves left arm*
*looks to the right*
"What is that?"
"..."
"zzz"

How do these things survive?

well, in trees is a good start.

That's how I am in the morning...

Fun fact about sloths... they come down from the trees to poop.
for some reason I have that urgently sung "gotta go, gotta go, gotta go." commercial jingle stuck in my head.

From YouTube description:

We came across this three-toed sloth struggling to cross the road between Arenal Volcano and San Jose. We formed a loose cordon to keep cars from running the guy over. He made it, slowly.
Story and photos at dolanbrau.com
Look for 'costa rica and the galapagos'.

To answer some questions in the comments:
a) it took 5-10 minutes for the sloth to cross half the road
b) it was covered in bugs and algae and had long sharp claws - no way were we going to pick that thing up

From http://en.wikipedia.org/wiki/Sloth:

On the ground their maximum speed is 1.5 m (5 feet) per minute. They mostly move at 15-30 cm (0.5-1 feet) per minute.

True Facts About Sloth[ses] has been added as a related post - related requested by PlayhousePals on that post.