Pretty much nothing...
I believe Darkcoin will be the #1, go-to, anonymous coin as it will have Masternodes, Ring Signatures, and I2P, while forks of Bytecoin such as Monero, HoneyPenny, Quazarcoin, etc will be lesser anonymous coins.
Masternodes: allows a bad actor to DDoS the legitimate nodes whilst maintaining a private network of their own nodes, and being able to observe and control the mix of transactions. It would be extremely trivial for law enforcement to create the semblance of anonymity whilst being able to fully monitor and control it, all because of the convenience of masternodes.
Ring signatures: I hope Darkcoin implement ring signatures in less than 6 months and in a manner that is not overly kludgy. The more coins that use the technology, the more refinement it goes through, and the more we can address challenges together.
I2P: we have decided this is a non-starter - forcing clients to run Java just introduces an additional attack surface and a set of dependencies. Monero already works through TOR.
I'm sure Darkcoin won't depend on the Masternodes for anonymity as much once Ring Signatures and I2P are implemented. The nodes might just serve as an incentive to help maintain the network...unlike Bitcoin where hosting nodes does nothing to help you personally.
I2P, while java may introduce additional inconveniences at first, I don't see much of a threat, especially when it can be improved upon over and over with Dev's like Evan...
So overall, masternodes might be an incentive, while the I2P and Ring Signatures are the real anonymity...still leaving Darkcoin ahead of the competition.