I think Things "Today" feature is a major strength and something that OF can't match on the iPhone. Today integrates sceduled tasks with manually selected tasks in a unified, simple view that I find very usable. Using Flags in OF doesn't replicate this. Setting the Start or Due dates on items can achieve something similar but it's far more cumbersome than the "Show in Today" mode of Things. The Next view in Things, although less structured and less powerful than OF, works very nicely and rapidly as a daily review mechanism, allowing for very easy allocation of tasks to Today.
It's not my intention to promote one app over the other--horses for courses and all that--but I'd dearly love to see OF maintain it's finesse and power while gaining some of Things elegance and simplicity. If OF ever allows the combined viewing of Due and Flagged items then it will be wonderful, at least for me.