I am both positive and negative on it.
It's useful and fun to a large number of people and definitely has some non-trivial value.
Does it have enough value to justify this kind of money being plowed into it? That's where I'm not convinced. These are big numbers and for them to ever make a return the revenue growth would have to be really really huge. I can't see Snapchat becoming Google or Facebook since its interaction profile is too narrow and brief.
We're basically talking about an ad-engagement and profiling medium here.
Google has huge value as an ad platform because they serve ads at the time of maximum intent -- their ads are targeted to what you are looking for right now and so they're more likely to convert than ads served at random times.
Facebook has huge value as an ad platform because they have so much data to target ads accurately and gather metrics about who engages with them. Many people use Facebook ads not as primary ads to drive conversion but as 'probes' to develop customer profiles, so it's almost like a focus group as a service.
What monstrous value is Snapchat going to provide in this space that will generate returns higher than the S&P 500 on many billions in investment over the next, say, 10 years?