As a nascent entrepreneur, my team and I have been knocking out projects for about 1.5 years. Some better than others, but we have a few minimum viable products (MVPs) under our belt (and from my experience comes my .02, buyer beware). With our latest project, I found that we were trying to build Rome. This was a mistake we made with our first product, it was pointed out to us by @Votizen's David Binetti and we've tried to avoid doing it again ever since. If for no other reason then to remind myself, "JUST FUCKING BUILD IT & SEND IT" & "DON'T BUILD ROME".
There is a huge emphasis on perfecting your pitch, the elevator pitch, the my company is X for Y and so forth. There should be as much, if not more, emphasis on building just enough to see if your product has a market / delivers value. In our case, we have an integrated solution for e-commerce. We have to add functionality to existing systems in order for our application to work. So our barrier is higher than most. But, if you are building a social solution, my advice to you is think ABACUS (ancient mathematical tool you played with in grade school).
The abacus was around for thousands of years because it got the job done. Later it was replaced by the slide rule, then calculator and now the calculator app...but it got the job done so people used it. When you deliver value to a group of people in need, some portion of that group will use your product. Then, once you've attracted some...focus on making it better to attract more.
If your team is arguing about whether or not you'll lose more people b/c you don't have multiple login services setup, just get Facebook going and move on. If you don't have Facebook and Twitter sharing setup yet, guess what? If your app sucks, people won't share it anyway...time wasted installing those buttons / delaying your launch is time you'll never get back. And don't add any 'You Can Also'. Let me repeat...NO YCAs. As a startup, your product does one thing. If no one likes that one thing, take it down and do another. No user will look past your first crappy offering to try some other (crappy) thing. You have like 5 seconds to deliver value...otherwise they are gone forever. First time users of web / mobile apps don't have time to figure stuff out...it's your job to make it so simple they don't have to think twice about how to use it. When you are big you can add other stuff, when you are a startup you have to be focused on one thing at a time...