I'm a pre-pharm student at Purdue and I have applied to the professional program there for Fall '06. Purdue doesn't require the PCAT, however many of my pre-pharm classmates are applying to multiple schools in case they don't get in at Purdue. They all went to Butler to take the PCAT since it's fairly close to Purdue so that's probably why there were many people from Purdue taking the PCAT when you did.