I'm new to web design and have been trying cross browser testing services and I am amazed that yours is so fast and so free! Thank you.
One brief suggestion:
What would you think about adding a time offset field, to (optionally) wait several seconds before taking the screen shot?
In my case, I am trying to figure out the Disqus (disqus.com) problems under earlier versions of MSIE but an instant screenshot does not allow Disqus to load (and display its errors) so I learn nothing.
Could you add another field (default = 0) beside the vertical offset where a user can specify a number of seconds to delay before taking the screenshot? This small addition would help many, I am sure.