Yes, it is down.
It was not working correctly, the script was a little broken, as some real items came up as fake, and vice-versa.
Plus the serial checker was run on a different hosting and server, which i didn't have 100% control over, as such could not fix the problems.
And it was costing us a few hundred ever 3 months to keep it and running, so I recently decided it was best to shut it down totally.
We are working on a new system for when we start rolling out some new products soon.
In the meantime, I have no way of knowing if your number is legit or not, most likely it is, and if you bought it from one of our official resellers it should be.
Thanks.