try using a production release (the minified version of ember.js), it uses a significantly faster get.
Are you rendering some very large lists? If so look into using List View.
If you have a ton of fields being bound that don't ever change modify them to be unbound.
{{unbound someField}}
If you are having some weird issue where a template is taking a long time, yet you aren't sure which one it is, you can add some timestamp logging to the beginning of your templates to track down the culprit. At the bottom I whipped up a quick helper. In your template you could use it like so. It will print out a timestamp with that data point passed in.
{{logTime this}}
{{logTime name}}
Ember.Handlebars.helper('logTime', function(someField){
var d = new Date,
timestamp = d.toTimeString().replace(/.*(\d{2}:\d{2}:\d{2}).*/, "$1") + "." + d.getMilliseconds();
console.log(timestamp + " - " + text);
return "";
});