Another startup operating in this domain is http://saaspose.com they offer Restful API's for many different conversions and document manipulations, plus basic plan is super cheap.
I have a feeling the parent works for Aspose, the site he is plugging. I use Aspose at work, so I find myself spotting these responses whenever something like this is brought up. Every time, an Aspose employee responds, plugging Aspose without mentioning that they work for them.
Aspose is pretty good, as it does not require Office interop to function. We've hit some limitations with it at work, such as dealing with PDF attachments and larger file sizes.
But anyway, yea. I just wanted to note that I think the parent poster works there. I made a similar response a while back and they actually Tweeted me in response to it, so I know they're on here. :)
