Despite the best efforts of book designers, proof readers and editors, a few mistakes sometimes slip into print. Below are some of the ones noted so far in Rough Magicke.

Pg. 3, "more than a hundred and thirty years before"
While this phrase is technically correct, something like 158 years actually passed between the pioneer settlement and the time at which Jonathan is speaking, 1992. Cf. page 344.
Pg. 19, "after sixteen years"
Jonathan was graduated from AMA in 1970 and began Cloyne Divinity School in 1974 (cf. page 31). If he has been teaching at AMA for sixteen years, he would seem to have graduated from Cloyne after two years: not impossible, though the Master of Divinity degree is typically a three-year program.
Pg. 54, "Mightn't here be"
Mightn't there be
Pg. 56, "rumors got through the corps"
rumors go through the Corps
Pg. 86, "to my surpass"
to my surprise
Pg. 104, "for it we have been joined"
for if we have been joined
Pg. 119, "lifting his coronet to his lips"
It seems unlikely that the bugler was making music on a piece of princely headgear: read "cornet," rather than "coronet"
Pg. 162, "Academy road"
Academy Road
Pg. 186, "Aubenaubee Bay"
Glenarm's Bay. Cf. pp. 7, 280.
Pg. 252, "David's mind"
Lee's mind
Pg. 280, "Cressy"
Not, in fact, an error: Dr. Davies is deliberately using the medieval English form of the name, rather than the French "Crécy."
Pg. 366, "road 35"
Road 35
Pg. 371, "Are going to look now"
Are you going to look now
Pg. 385, "Café du Monde"
The actual New Orleans-themed restaurant in the real Palmer House Hilton™ is called "The French Quarter," and apparently does not serve beignets, those specialties of The Café du Monde™ in New Orleans' Jackson Square. This is one of those oversights of reality which fiction has the privilege of correcting.
Pg. [411], "My thanks are due"
Ironically missing from this list is Mr. Lewis Kopp, of the Culver Academies, who provided several absolutely last-minute corrections.