It was still working up til today. Unfortunately this forum isn't optimised for mobile so I keep ending up in the wrong section. I hope this gets fixed soon as the Arena is now all but unusable.
It still worked for me for quite a while after it was announced, but I had to reset the actual Tapatalk app on my phone and after that I couldnt get back into the arena.
Its been interesting for me, I only joined the arena recently, and I didnt get a good feel for it until I started using Tapatalk, so this has forced me to learn to effectively use it on a normal browser. So as much as I love the ease of Tapatalk for being a pony addict while Im at work- its been good to learn to use the arena in its original state.