If there is one thing I really feel deifnes this format, it is little synergy. This is related to the topic i talked about a long tme ago: redundancy (found somewhere on the commonist party clan site).
Little synergy is the reason the decks that win do. Take for example, MBC. The version I run is a touch more tool box than most. But there are tons of little synergies. I run shinobi with ravenous rats, gravediggers, and ragers. I also run a lone urborg uprisings. Why? it draws a card and recurs a dude, mostly a twisted abomination that was cycled to get a swamp which was used to fuel a large corrupt. While this seems like normal game affairs, it is actually an example of little synergies.
Little synergy (LS) is different than deck synergy. LS relies on pockets of cards interacting well with each other rather than the entire deck functioning as an organism. Organisms include tribal decks, affinity, and other decks I can't think of right now. Everything in the deck works with everything else. IN LS decks, pockets work independantly, but can overlap. This allows for more versatility while not losing a ton of consistancy.
TDR, my original version, unknowingly used this principle with the inclusion of sparksmiths. They had LS with the cohorts and the goblin sledders. While it worked in the deck overall, it also had it's own pocket.
Now I'm not saying putting LS in all your decks will make it win, but it make help with certain aspects. A good example would be in the ever present RG aggro.
Llanower elves create little synergies with Horned kavu. So do skirk maruader and phantom tiger and kavu climber. This is one pocket, but it does so much.
Similarly, a card can have little synergy with a deck. In RG aggro, this would be Horned helm. It can do so much.

Any comments? Please tell me what you think.. tell me your own stories of little synergies.

The best example of synergy I've seen in a game was to put combat damage on the stack, Repulse one blocking who was going to die, drawing a Basking Rootwalla, who is discarded to pump a blocking Wild Mongrel and save him too. Ended up being a 3-for-1 if I count it correctly (-2 opponent's creatures, +1 Basking Rootwalla, all for the cost of one card). I think my point is that anything with "draw a card" on it is likely to add to your synergy, once you've got the mana.