Besides the fact that it's free? :-)
Here are a couple of scenarios from our current users:

quick way to test cross-browser look-and-feel for your company/client's web pages
See the list of browsers and resolutions above that we support. Using our service also means you don't have to have different browsers set up in the office. Just outsource that problem to us instead.
avoiding the proxy at work
The less we say about this one the better I guess.

Currently we are rolling out phase 1 which includes the basic emailing functionality, but our phase 2 has already begun and will introduce the following:

Firefox extension
user profiles
online viewing of browser results
result histories so you can see how your site has changed over time
better integration into your testing environment via Firefox plugins and 'tester' roles on this site

I've just sent an email, now what?
Shortly you will get an email from our servers with a screenshot (Jpg) attached showing your chosen URL in the browser you selected and at the resolution you wanted!

How long until I get a response?
You should get your response within 2 minutes.

No reply yet?
We're still in beta, please email our support and we should be able to find out what's happened to your request.

Like to join our team?
Send us an email with some of your ideas and we can chat.

WTF?
Exactly.