Wolf Rentzsh offers a behind-the-scenes look at Textcast:
Textcast is a deceptively simple app. It’s aim is simple, but it unifies many disparate technologies and applications which leads to lots of complexity under the hood. It’s one of those projects where you can get the basics working inside a weekend, but it takes months to make it a real Mac app.
Be sure to check out the end of the article where he lists links to several great Cocoa resources.