For those of you hoping to get in on some PTR testing this evening, you'll be happy to know that you're not alone in your "Trials of the Instance Not Available" raid. Lord Jaraxxus was supposed to be available for the US this evening, which is the 10/25 man raid boss.
Add to that 3 points into Spiked Collar and you now just gave Fido an additional 9% damage on all of his attacks.
The tier three talents might look a bit lackluster, but think of putting 3 points into Avoidance for the 75% reduction in damage from Area of Effect attacks as added insurance for pet survivability.
Your next choice is going to be three points into Spider Bite for a 9% increase in your pet's chance to land a critical strike.
Daelo has posted that Blizzard has had some technical issues with the testing tonight, and that things are being delayed until they get fixed.
WoW.com has a group assembled and will be going in when the darn things works, and hopefully we'll have some good guides for you in the next couple of days.