Ideally, how much AP should your Q have farmed up, at the 10 and 20 minute marks?
100-150~ by 20 minutes. Ideally, you should be lvling the hell up out of W and some E after your lvl 1 point in Q.
By the 15~ minute, the enemy is usually pushing harder than you can Q spam. using a W will wipe out all casters and weaken melees enough for you to Q.
© 2013 Riot Games, Inc. All rights reserved. Riot Games, League of Legends and PvP.net are trademarks, services marks, or registered trademarks of Riot Games, Inc.