First of all, looks good.

I would suggest a few things: Let me make a list w/o signing up. (check out how stack overflow does anonymous stuff..it's good.) Don't tell me "there's no post-signup xxx" and then make me confirm my e-mail. (for that sake, don't make me confirm my e-mail, use oid or something, what's my e-mail really worth to you anyway?) "You've been activated (hopefully)" -- Unsure your software works? Don't make me login after I activated. This is three times I have to put my password in before I can use it. What is the exclimation icon next to an item? Advertising your competitors? are you sure? How are items sorted? They're not draggable, but they don't seem to be in a instantly recognizable order either. Could I get a hover state on the bin so I can tell that I'm going to commit to an action? Could I undo the bin?

Re: twitter. Here's the way I did it. 3 step process. first, you must follow me. second, input your twitter name on my site. Third, I send you a dm, you input the code to confirm, that's it, now you're tied.

That's all I have at a quick glance. Looks good, with a good api, and a simple purpose.