Common sense warning
Before I start this post let me outline this is my opinion and you may or may not agree with it. However if you want to discuss it with me in the comments I will be more than happy to, but please respect each others opinions and views and don’t start an angry flame war.
OK enough of the common sense stuff lets get to it.
I personally think you are doing it wrong if you are using alternative templates in Version 6 of Umbraco to return JSON or XML for example.
So read on to find out why and the approach I think you should be using.