If the site says “Don’t worry, we won’t give out your info” that’s not very believable (yet people do it anyway).

In fact, if you want to harvest Twitter accounts, make a semi interesting tool, and do just that.

I’ve seen similar issues with Gmail accounts (log in and we’ll check to see if your friends are on our service). Google fails at this as well by not providing a custom address book feed. This is a simple fix. Enter the url of the site asking for your contacts, Gmail generates a unique url w/random code (for that site’s URL only). You’d have to do this for each site that asks, but that would lock it down so the url can’t be given out (granted if the site is shady they can just strip that list and do whatever with it) but it does give the user some safety and they never have to give out their login info.

The “Web 2.0″ world is really just a bunch of suckers, that are way too trusting with their data.