Twitter, Apple, Facebook: The perils of building on someone else’s platform.
stevenwei.com
stevenwei.com
URL shortening especially just amazes me... if twitter ordered some pizzas and stayed back late tonight they could kill that mini-industry.
B. Start from scratch. Spread by word of mouth. Try to get media coverage. Risk getting lost in the crowd.
C. Start off building on top of one of those platforms to get a jumpstart on gaining audience. But plan your strategy so you aren't dependent on them, and have a stable future even if they disappear completely tomorrow.
Some services (like url shorteners or photo uploaders) that are entirely dependent on the platform to be useful probably can't work in that model. To them I would probably say: get big and hope to cash out before it's too late.
The one exception to this might be Zynga, but of course they're far and away the #1 app developer and I'm sure some non-trivial percentage of Facebook users come back to the site just to play Farmville.
Build your own offering. Use platforms to reach customers, to spread the word, as service. Be ready to stop use any of them overnight.