You're using the incorrect syntax to pass named parameters to your handlebars helper. What you want is something like this:
var data = {
"attributes": {
"name": "name"
}
}
var templateHtml = '{{textfield name=attributes.name}}';
var template = Handlebars.compile(templateHtml);
var formHtml = template(data);
And an updated fiddle: http://jsfiddle.net/3yWn9/1/