Should entrepreneurs just give up on their app ideas, simply because Facebook could eventually clone them and crush them with a billion users? Of course not, and anybody who thinks that Facebook (or any other big company) cloning a startup's product spells Armageddon for that startup doesn't know what they're talking about.
Remember when Facebook tried to make a Foursquare competitor? How about the time it tried to make a Groupon competitor, and it went nowhere? The same is true of its Quora competitor (Facebook Questions) and even its Craigslist competitor (Facebook Marketplace).
I could go on and on, but the point is clear: a big company launching a clone can be scary, but it doesn't mean Armageddon. There are two other factors to consider: defensibility and vision.
My point is this: it takes a lot more than a clone to take out a scrappy startup. It also takes a long-term commitment by a juggernaut. Don't be afraid of the juggernaut entering your market, entrepreneurs. If you have a long-term vision, focus on defensibility and build faster than the competition, you'll eventually become the juggernaut.
"As long as u have a good product and is accessible (damn those with 10000 page registration), combine that with complete dedication and competence, there's no need to fear. Quality and word of mouth goes a long way."
Read more of why startups shouldn't be afraid of Facebook cloning them:
http://news.cnet.com/8301-33617_3-57560622-276/why-startups-shouldnt-be-afraid-of-facebook-cloning-them/