I imagine this situation:
An adversary does nothing but generate new blocks without including any network transactions for 50BTC reward block after block in an effort to outrun the main block chain. They could take their time because unnecessarily increasing block output would only increase their complexity and they don't need to make it harder than they have to. They do it long enough to collect sizeable booty.
They don't participate in the rest of the network and don't announce their chain. They increase their network capacity without letting the network know. In one 2 week window when they are certain that their chain is longer than the official chain they release it out to the public and it is adopted as the main chain (invalidating lots of legit transactions along the way). They then try to quickly cash this out like it was done on MtGox. Even if they didn't want to cash out, kids like LulzSec may decide to do this just for fun.

Are there any mechanisms in place that stop clients blindly adopting the longer chain if the differences are too great? Would some damage control algorithm kick in? Is there a way to detect a "bastard" chain that sprung out of nowhere?

I know this sounds unrealistic, and nobody would compromise their investment into economy in this way. But what if someone had a reason to do this anyway.

Hopefully by the time BTC becomes mainstream it would require a google-size mob to do this kind of damage and they wouldn't be interested in any of that. What's stopping "The Fed" from doing it now?

Would such an attack be possible today?
I would imagine that something like this has been discussed already.

Here's a conceptual approach for merging two or more block chains that are created as a result of lack of network connectivity between parts of a network.

http://bitcoinery.tumblr.com/post/6731628999/how-to-merge-bitcoin-block-chains

Essentially, the suggestion is to not simply discard smaller chains, but to merge the differences back into the longest chain. This maintains all existing properties of bitcoin.

Hi Guys,

I've written a blog post about Bitcoin's problems as I see it.
There may be a few misconceptions because of my only recent introduction with the subject.

Please feel free to suggest answers or corrections if you have any.

http://bitcoinery.tumblr.com/post/6653365245/bitcoin-problems-that-need-to-be-fixed

Cheers!

Hi All,

Please commit to starting a new StackExchange Q&A website for Bitcoin.
You know how useful Stack Overflow is, let's get the same for Bitcoin.

Please go here and vote for starting a new Bitcoin site:
http://area51.stackexchange.com/proposals/30763/bitcoin-crypto-currency

This would solve the troll problem and the newbie restrictions would not be needed. We'll also get a better interface.

The fact that smart (new) people can't participate in other discussions doesn't do any favours to this forum.
When I see a nice comment, I'm not going to the Newbie forum to post a reply.
I guess this attitude is the reflection of the 'early adopters are superior' mentality that is not the good side of the bitcoin idea.