Indeed, if it is doing pretty well to correct typos, it sometimes tends to suggest false corrections, or even worse, to suggest corrections when there is nothing to correct... For example, on the French version, by default, self-correction will replace .fr by .de when typing an URL, or will had accents where they are not wanted, because it generally favors accented words since they are more difficult to type directly. Moreover, when a space is entered, it is automatically the suggested correction which is taken into account, to dismiss it you have to click on a small cross, not always easy to aim...

Thus, many users are bored by this feature, and some of they decided to launch a petition, asking Apple to add an option to disable this correction in the system settings. If you are you also embarrassed by this feature, you can sign this petition until September the 30th on Please-let-us-disable-autocorrection-steve.com. Over 16 000 people have already signed.

If you own a jailborken iPhone, that possibility is already offered by the software BossPrefs.