The acquisition of WhatsApp will have a positive impact on Facebook's stock. It's a cross-platform messaging app, which Facebook will find a lot of use out of. It will increase Facebook's efficiency, or if the company is going to be kept separate from Whats App, then it will still be profitable as a separate platform.
With appealing to a wider user-base, Facebook stock will rise. The company is appealing to people who like to text, and by purchasing this app they are expanding the market of what Facebook has to offer. It could also be thought that Facebook already offers this through the messaging in the site.
Facebook's acquisition of WhatsApp was initially met with a negative reaction in the stock market, however the technology and value add that WhatsApp brings to the Facebook social network will definitely have a positive impact in the company's stock price in the long run. As Facebook expands it's services to rival that of Google and even eventually retail companies such as Amazon, acquisitions such as WhatsApp will begin to make more and more sense.
Yes, I do think that this app getting took away will do a lot of good for face book. I think it will get rid of a main competitor of them, so they will get more people back, and they will get whole lot more money out of this deal.
I do not think it will add no more users to Facebook, meaning no more new customers. I think Facebook has reached a plateau. Some think it might bring Facebook next billion customers, but just do not see how a chat app can be that cool. Of course, I have never used it so I would not know.