Come code at Twitter's annotations hackfest
engineering.twitter.com
engineering.twitter.com
See you there ;)
I actually run a (quite profitable) social media app that works with Twitter.
But based on the last 6 months of API changes, I'm going to shut it down. I'd rather direct my energy towards something that I have 100% control of, rather than hobble on making little concessions here and there to comply with Twitter's ToS, as their platform matures. The long term picture doesn't look good for any Twitter app, really. Although on a long enough timeline the same could be said for building on any 3rd-party platform.
Like you say, nothing wrong with what they are doing - it's just good business - but I don't want to keep jumping through hoops anymore.
Building on Twitter was good fun, though. And it certainly helps early traction. But as time goes on and your app starts making more money and you start getting more serious about running it as a business (as opposed to a hobby project), Twitter becomes a liability, not an asset.
YMMV.
That and, none of the customer subscriptions are transferrable. The new buyer would only earn money from new customers.