I've signed up.
Last MMOs I was subscribed to were EverQuest and Dark Age of Camelot back in 2002.
Since then I've been in Beta tests or free weekends or trials for Star Wars Galaxies, Rift, Guild Wars 2, Star Wars: The Old Republic and The Secret World. And even some lesser known MMOs, although mostly due to my IGN Prime subscription or Beta-key give-aways which gave me access to beta's regularly.
With the exception of Star Wars: Galaxies I've never signed up for a beta before TESO.
But none of them have caught my interest so that I would buy them (you still have to buy Guild Wars 2 to play) or subscribe. Even though most of them have gone FTP, that still wasn't enough for me to really get into them, I still enjoy single-player rpgs too much.
The only MMO I'm investing some time in at the moment isn't even an RPG (It's Planetside 2).
But since I like the universe and lore of The Elder Scrolls so much I just have to play TESO (eventually, I will play it even if I won't be in the beta), although I'm pretty sure to get annoyed because of lore choises they made.