Maybe this is old news, I don't know, but after watching Brad's latest interview with fourzerotwo, I'm thinking Martyrdom isn't going to be in Modern Warfare 2. He seemed to imply that they took it out, and replaced it with their "Death Streak" system. Which really has me bummed. 
Some of my most enjoyable kill streaks in Call of Duty 4 were because of Martyrdom. I'd rush in, kill 3-4 guys with my gun, kill a couple more with a thrown grenade, then die in the middle of 2-3 more guys, drop a Martyrdom grenade, and promptly kill them also. This happened all the time for me, and led to a pretty decent Kill/Death ratio.
 
Now, I am perfectly aware of what most people think of Martyrdom. They call it a "noob" perk, or something to that effect. They label it as something only worthless players use. Imply that it's a handicap for a bad player. Etc... That just makes me want to use it even more. I know this is going to make me sound like an ass, but nothing brought me greater enjoyment, or made me laugh harder, then when I'd kill someone with Martyrdom, and they'd get foaming at the mouth angry about it. Then send me a hate filled message. Cracked me straight up.  That's also the reason I used the grenade launcher all the time, or "noobtube" as most call it. Because it just infuriated some people.
NEWSFLASH! I'm always going to make a point of finding out what weapon/tactic people hate the most, and then do nothing but use that. Simply because you whine about it all the time, and that just makes me want to use it even more. You can label it as whatever you want, but I actually think of it like psychological warfare to a degree. Odds are, if I get you extremely pissed off, and blind with rage, you aren't going to play so well, and I'm going to win. Mission accomplished.
 
So anywho. Long story short. I like Martyrdom. It resulted in some hilarious, really priceless moments in CoD4 for me, and I'll be sad if it doesn't show up in MW2.