I kinda signed up for this forum and forgot about it for like 6 months... ironically I've been posting on JB's forum. Jay is one of my most personally inspiring drummers. A lot of you guys are talking about how educated he is. A lot of people don't know this, but he only went to Berklee for a year (it's like $40k a year with room and board...). And yes, a yr at Berklee is still a YEAR at Berklee, but I'm saying that's just a small part of his getting to the level he's at.
You can go to his website and ask him - he will never claim to be the fastest drummer out there. He'll tell you he's a metal/thrash drummer. One of his biggest influnces is Benante from Anthrax. Jay actually filled in for him for 2 shows when CB recently had his baby - that's how much he's played along with Anthrax growin up. You can hear that in a lot of his beats as well.
The biggest thing I love about his drumming is that he writes drum parts that fit the song as best as he can - and that's the most important thing that we as drummers must do. There are some things about his parts that you can't tell as well from a quick listen as you can by really studying the song. If you haven't seen his 'drum lesson' on the dvd that came with The War Within, I'd recommend it. It gives you a greater appreciation for some of his parts. My two favorite songs of his are "The Light That Blinds" and "Ghost of Past Failures." In the latter you will hear a lot of the MD solo parts at work, like the tom pattern where he keeps the beat on the x-hat, the tom pattern,8ths on kicks, snare on 2+4. They're not impossible for others to play, but that's not the point. He's a making great music.
Also, for those of you who are real big into speed - to quote Jay (from a thread where people signed in as guests were coming on and anonymously comparing JB and Joey), "on the new SHAD record there's a Double kick song at 210BPM but I bet that's still not fast enough!!!" Obviously, the man is progressing, just like the rest of us.
(for comparison reasons, the light that blinds was recorded at 180bpm)
p.s. I'm a big fan of Alder as well, I just picked up Ashes of the Wake last week.