Here's an email I got from somebody worried about MasterCoin clones:
On Thu, Sep 12, 2013 at 4:28 PM, John ----- wrote:
Hi JR,
I just listened to your talk with the bitangles and am concerned with your current protection against being "forked", which is probably the wrong word choice, but provides a nice pun for what could happen with the introduction of alt-MasterCoins.
Bitcoin would not have the same first mover advantage if an alt-coin was created two months after Bitcoin. The moment someone sees any value to Mastercoin, then they will either consider buying Mastercoin on the open market, or copy the source code and create their own Exodus address.
Thoughts???
John -----
MasterCoin is vulnerable to clones, although the problem fades as the MasterCoin project continues to gain momentum.
It's helpful to try to imagine the uphill battle a clone would face. Who would launch it? The number of people who have the reputation to launch something like this isn't huge. Would anybody take them seriously? If you were an investor, would you send money to a cloned project with it's own Exodus Address?
A clone would have to offer some MAJOR innovations, and they would have to move very fast. In all likelihood, we would blatantly steal any innovations we saw in somebody else's clone, which I have said multiple times, in an attempt to discourage people from trying it

JR,
You don't have to mask my name. I only send via email so not to sound like a troll, but more like a subconscious. I do accept tips if you value any of my opinions (a shot out to Adam B. Levine's Project Watershed).
Why do you think that MasterCoin's vulnerability to clones fades as the project gains momentum? I suspect you are right, but... According to BitcoinMagazine, Tonal Bitcoin, the first alt-coin, did not come out for 2 years after Bitcoin. I did not read why Tonal Bitcoin failed. I do not think Mastercoin will be granted anywhere near that amount of time before something nefarious is attempted.
Does anyone else have any thoughts on this or other attack vectors that Mastercoin investors should try to protect themselves against?