Muggles' Guide to Harry Potter/Magic/Obliviate

Overview
Obliviate is the verbal component of the Memory Charm, a spell which allows the erasure or modification of memory.

Extended Description
First seen when Gilderoy Lockhart attempted to use it on Harry and Ron, this spell, when done correctly, apparently allows a substantial amount of control over the subject's memories. We see it used a number of times through the series. The most prominent times are:


 * as mentioned above, in Harry Potter and the Chamber of Secrets, when Gilderoy Lockhart attempts to cast it on Ron and Harry so as to allow him to claim to have defeated the Monster in the Chamber. In this case, he is using a broken wand, which backfires; as a result, afterwards he is barely able to remember his own name.
 * in Harry Potter and the Goblet of Fire, when the Muggle keeper of the campground has his memory changed so that he forgets the odd magical things that he has seen the occupants of his campground doing.
 * in Harry Potter and the Order of the Phoenix, where Kingsley Shacklebolt casts it on Marietta Edgecombe so that she forgets that there were previous meetings of Dumbledore's Army.
 * in Harry Potter and the Deathly Hallows, Hermione casts this spell on a pair of Death Eaters and an innocent waitress so that they will not recall having seen Harry. She later uses it against Xenophilius Lovegood to make him forget the presence of Ron Weasley.

Like so many spells, a large part of the effect of this spell very likely depends on what the caster is thinking at the time the spell is cast. Presumably the caster must hold in their mind a representation of the memories needed to be changed, along with what the memories should be changed to.

Analysis
Apparently, this spell is most often used to clean up any 'spillage' in front of Muggles. The International Statute of Wizardry is specifically designed to try and keep the Muggles unaware of the Wizarding world, so this spell is apparently reasonably often used on Muggles to keep them unaware of what the wizards have been doing.

Questions

 * 1) Is there a way to reverse the effect of this spell?