This deck has come onto the scene with great results in big tournaments in the last few weeks. I'm going to start with a deck list and then explain why it works and go into some matchups:

Johnny Niemeijer's Jund Blood

Standard - 4th place, 2009 Netherlands Nationals

Land: 24

4 Auntie's Hovel
2 Fire-Lit Thicket
4 Forest
4 Gilt-Leaf Palace
2 Mountain
4 Savage Lands
4 Twilight Mire

Creatures: 22

3 Anathemancer
4 Bloodbraid Elf
4 Boggart Ram-Gang
3 Chameleon Colossus
4 Putrid Leech
4 Wren's Run Vanquisher

Spells: 14

4 Jund Charm
4 Lightning Bolt
3 Maelstrom Pulse
3 Nameless Inversion

Sideboard:

1 Anathemancer
1 Chameleon Colossus
2 Deathmark
4 Great Sable Stag
4 Infest
3 Thoughtseize

Card Explinations:

• Anthemancer- With alot of decks running non basic land (for example this one running 18/24 land nonbasic) he comes into play dealing alot of damage. This guy is a pure metagame card currently crushing the format. Of course he will be the first guy you want to take out against someone running only basic lands.
• Bloodbraid Elf- Cornerstone card in this deck. His ability gives you insane card advantage. Also makes things no fun for anyone waiting to counter your spell. Most of the deck is run around this card costing 3 or less mana. only exceptions are himself and chameleon collosus.
• Bogggart Ram-Gang- One of my favorite beatsticks. Survives the board sweepers run in the deck and deals out some serious damage fast.
• Chameleon Collosus- Another solid beatstick. a bit more resilant then most creatures and something that has to be dealt with or he will end games.
• Putrid Leach- Your main 2 mana guy. Basicly every time you attack you will use his ability to make him a 4/4 (unless its pointless of course). Also pay 2 life to keep him from getting killed by sweepers and the like.
• Wren's Run Vanquisher- You other awesome 2 drop creature. Have to be careful with him though as revealing him with bloodbraid you will still have to pay one of his alternant costs. (dont forget your changelings are elves too)
• Jund Charm-One of my favorite spells in the deck. versitility is always helpful. if you dont need to sweep away weenies, you may need to deal with someone's graveyard (anthemancer esp), or you could always pump one of your guys permanently.
• Lightning Bolt- Nice spot removal, kills key creatures for alot of decks while you power out your own. If nothing else can always be thrown at your opponent.
• Maelstrom Pulse- Kills any non land permanent, this includes not just creatures, but any pesky enchantment, any artifact, and any planeswalker. This card can also give good card advantage if it kills something that has copies of it in play. Gets rid of tokens pretty well too.
• Nameless Inversion- Basicly more spot removal. This one doubles as being able to pump your leach. I honestly think there are better choices, but I guess it can work here.
• Deathmark- Simple yet effective sideboard card. gets rid of pesky forge tenders that may stand in your way. also kills alot of guys in your deck so bring it in in the mirror. (anti WW, anti elves, anti jund, anit bant)
• Great Stable Stag- Best sideboard card in the game against faeries. Also good against alot of control decks focused on counters or against decks running black removal. (anti fae, anti jund, anti merfolk)
• Infest- destroys most aggro decks but leaves yours mostly unharmed. only guy you have to watch for is bloodbraid (which if you cascade into it with bloodbraid infest resolves first then bb.) (anti elves, anti WW, anti fae)

Lets get on to the matchups: (win %'s coming from stats at us nationals, where 32 players or about 15% of the field was jund aggro)

• Faeries:68% win against fae. your deck is aggro and they will have trouble stalling you. running 4 main deck sweepers that just rock their board and some targetable removal will set you soaring above past them.
• White Weenie: 33% so they jund won 5 of the 15 matches played against White Weenie. From the board bring in your infests and deathmarks. wipe the board early and often. from the board they are going to bring in a pro black guy, hold lightning bolts for him and your black removal for forge tenders. good luck.
• 5cc: 56% wins against 5cc. Most of your guys survive the main used sweepers. 5cc may adapt and start running more actual wraths to make up for this so be careful not to over extend while still extending enough to put the hurt on. Anthemancers absolutely wreck them.
• Elves: 60% you will constantly sweep their board while pointing lightning bolts and nameless's at their key guys. they can be blindingly fast though so be ready. be careful what guys you burn away and sweep as often as possible.
• Red Black aggro: 37% wins. they start turn 1 where you really start turn 3 or 4. they also have discard effects killing your card advantage. They often don't care about their own guys but you still need to sweep their board as much as possible. I would put blightning of your own in the sideboard against these guys if you think they will be a problem.

Summery:

Jund blood aggro is a midrange aggro deck. against faster aggro decks you need to move into the controlling aspects of the deck often on the defence (not a place you want to be). Against other midrange aggro decks or control decks you need to come out fast and put pressure down, this is where you shine. If you expect alot of RDW (with or without black splash), white weenie, or similar decks, you may want to look into another deck. If you are expecting to find fae, elves, and 5cc, this deck can work wonders for you.

Good luck. Hope this has been helpful.