Yes, Firetask 3.0 is optimized for iOS 4 and includes a complete set of high-resolution images. It supports multitasking/fast app switching and looks even better than ever before on the iPhone 4's new retina display.
Your task will only appear on today when it really becomes relevant to you. A task becomes relevant when it is either due today or within the next five days, or if it is the first actionable task for you in a project.
The "Waiting for" category is a concept we borrowed from David Allen's "Getting Things Done® - GTD®" way of managing tasks. Basically, you use this category to keep track of tasks you are not doing yourself, but delegating to other people.
The "In-Tray" is a concept for storing your thoughts and ideas, things you do not yet know what to do about. As soon as you have decided what to do with them you can, e.g., make them "Actionable" or you delay them to "Someday" - simply by changing their status.
Currently we rely on Apple's iTunes backup, but we are working on a desktop version for the Mac which will be released shortly.
Firetask was originally designed and developed specifically for the Apple iPhone and iPod touch. However, we are working on a Web and/or desktop companion application in order to support syncing in the near future.