Now that you’ve gotten a preview of iPhone OS 4.0, here’s an in-depth preview, courtesy of Gizmodo’s Jason Chen. Good news: “it’s surprisingly usable – not nearly as slow as iPhone 3 beta running on iPhone 3G last year.” Videos after break.

Most of the new features we mentioned today are there, theoretically, but it’s not exactly usable until developer support shows up in apps.

[via Gizmodo]