1. A computer-implemented method, comprising: at a portable electronic device having a touch screen display: displaying a plurality of key icons, each key icon having an adjustable hit region of dynamically adjustable size; receiving a sequence of individual touch points input by a user on the touch screen display, wherein: each touch point is determined at lift off of a contact from the touch screen display, and an image with an enlarged version of a character that will be selected as the character corresponding to an individual touch point is displayed prior to lift off of a respective contact, wherein the character image that is displayed prior to lift off is selected in accordance with the adjustable hit regions of the displayed key icons; and after receiving each of the individual touch points: forming a user-input directed graph for the sequence of individual touch points received so far; determining a character corresponding to a last received individual touch point in accordance with the adjustable hit regions of the displayed key icons; displaying a sequence of characters corresponding to the sequence of individual touch points, including the determined character; and updating sizes of the adjustable hit regions for a plurality of the key icons in accordance with the sequence of individual touch points input by the user.