UPDATE 9/14/2011: TH_NK has updated Pottermore so that you no longer earn house points when you fail to brew a potion, this simple fix nullifies the cheating method mentioned below, Hurrah!
I’m going to preface what I’m going to say below with the statement that I am not putting this post up as an invitation to cheat on Pottermore. I would have sent this message privately to the Pottermore developers, however, I could find no place on pottermore.com, insider.pottermore.com, @pottermore, or Pottermore on Facebook where I could send a message to the devs. The closest I could find was the Beta Feedback button, which presents a feedback form that lets you rank a page on a scale of how much you like it, but it has no comment field and no way to introduce a comment for the devs.
My hope is that by posting this publicly on my blog, the Pottermore devs will find this post and fix the issue (and perhaps add a method of commenting privately to the devs).
So the problem with Potionmaking in Pottermore is that you can earn far more house points from failure than you can from success, at least in a given time frame.
If you successfully brew a potion, you earn 5 house points, but successfully brewing a potion takes a minimum of 85 minutes (different potions take longer, 80 seems to be the minimum wait time between the 2 steps and even if you are fast your additional time of actually doing the steps will take you an extra 5 minutes). While a potion is brewing for 80 minutes, you cannot brew any other potions (even if you own multiple cauldrons), you simply have to wait out the 80 minutes and then come back.
If you fail to brew a potion, you still earn 1 house point, as soon as you get into the potion-making session, and wave your wand, you’ll “fail” to make the potion, but will still be awarded 1 house point, but this takes a minute (or less). If you take 85 minutes of doing one “attempt” per minute, you will earn 85 house points, 17 times as many points as you could possibly earn in that same amount of time by brewing the potion correctly.
Granted, you will eat through the potion ingredients pretty quickly going about it this way, but if you stick to the “cheap” potions, that is to say, the potions that don’t involve expensive ingredients like bezoars, your hundreds of galleons given to you by Pottermore will last you for quite a few house points.
I know many other people have figured out this simple realization that you can earn more points through failure than you can from success, but what isn’t clear is if the Pottermore devs are aware of it yet, my hope is that if they aren’t, that this post will clue them in that the potion making process really needs some serious thought. As it is, there is next to no incentive (other than acquiring a vial of potion) to actually go through the lengthy process to create the potion successfully.