I have been very careful to avoid my husband getting anticholinergics, even when the urologist said he would prescribe one that didn't cross the blood brain barrier (I looked up some research and they were using the mini-mental to see if there was cognitive decline, which didn't impress me).
However, with Parkinson's it is a a matter of balancing drugs with opposite effects. Aricept (or Exelon) make movement and balance problems worse (and the antipsychotics can be even worse), while Sinement helps movement problems but makes cognitive issues worse and hallucinations more likely. The right balance is better than giving neither, but it is a matter of balance.
I was blissfully unaware of the anticholinergic drugs until I started investigating them a few months ago. Many of the common over-the-counter drugs we use have anticholinergic activity--antihistamines, antacids, antidepressants, antidiarrheal. The reason for my interest was that the GI told me to "eat what you want and take Imodium" for my diarrhea problem (caused by food intolerances).
An article about a study: Anticholinergic Drugs May Increase Cognitive Decline http://www.medscape.com/viewarticle/573208 EDIT: I find that the Medscape entry will just bring you to a login-in page. If you enter the study name in Google it will bring you to the study.
For a listing of anticholinergic drugs: developed by Indiania Univirsity http://www.indydiscoverynetwork.org/AnticholinergicCognitiveBurdenScale.html