AFAIK, Twitter doesn't offer a sensible API for twitter services to use, such as having the user create a unique key which gets sent to a service, which then uses this key as authentication. The user (and twitter) would then be able track all activity based on that key, let you disable that key, etc. As a result of this, every Twitter app that needs to access your account asks for your username and password.
And, now, your Twitter account can have money in it?
Besides the obvious question of "is this really useful?", which I presume the answer for a lot of people is: "Yes! You can show off you paid someone... on TWITTER!!!!", it seems to me having funds tied to a Twitter account is a big mistake. Like Facebook, the default login is not secure, upping the ante for sniffing a cleartext password from just denting your social life to liquidating whatever funds you've put in your Twitpay account.
That's why Twitpay didn't go the "put funds into your account" model. We're powered by Amazon Payments, and to settle up and move actual dollars requires logging in to Amazon and approving the transaction. We're actually one of the more vocal critics of the "give out your Twitter password to any and all services", so we designed Twitpay to avoid the issues around that.
This bothers me about EC2 as well. Most efforts don't get how useful (and headache saving) delegation-of-rights functionality is. This should be part of everyone's toolbox by now...
You don't have to settle up immediately, though. We see this being really useful for people who pay each other back and forth. Run a tab with your friends, and only settle up when one of you needs the cash.
And yes...the Amazon Payments setup is a little rough. We're giving them feedback to see if we can smooth it out a little.
And, now, your Twitter account can have money in it?
Besides the obvious question of "is this really useful?", which I presume the answer for a lot of people is: "Yes! You can show off you paid someone... on TWITTER!!!!", it seems to me having funds tied to a Twitter account is a big mistake. Like Facebook, the default login is not secure, upping the ante for sniffing a cleartext password from just denting your social life to liquidating whatever funds you've put in your Twitpay account.