accidental use of magic (was Re: Did Harry Apparate?)

[aprilgc at ivillage.com]

No: HPFGUIDX 15441

<snip>  Speaking of which, what about how harry turned his teachers wig 
blue? <snip>
> -Rachel

Another question - can we assume that the department of magical mishaps 
(not the correct name, but I like it <g>) has been running around 
cleaning up (memories) after all these incidents?  Does Harry's teacher 
(and anyone who saw/talked to her remember this only long enough to 
write the note (same goes for the headmistress in the chimney 
incident)?  Do the department people modify their memories shortly 
after?  What would happen if the Durselys responded to her letter after 
her memory had been modified (assuming it was)?

Along that line, do they round up everyone who was in the reptile house 
and Piers and family, and modify them?
a.
if covered, please point me to the thread.