This of course depends on the quality of the hammock, in much the same way that a poor mattress will make for a bad sleeping experience. I own a Warbonnet Blackbird hammock (http://warbonnetoutdoors.com/blackbirds.php) and it's extremely comfortable. They're one of the very best hammocks out there and are very popular with the backpacking crowd.
Even though it wasn't the best sleep, I could bear it. But the friend I was with couldn't take it, he wanted to leave at 5 in the morning the first night there, he was totally desperate.
From that experience I'd say there's no way hammocks make sleep easier.