And you think over 80MB of memory usage is considered normal? The memory limit is set to 64MB which is plenty, since the typical memory usage is less than 30MB for the entire website to run. Something as simple as confirming a registration should not take up 80MB of memory.
Removing the Manager user group (id 6) did not decrease the average memory usage of the website, but it seems that CB conflicts with this user group, causing it to spike. It seems others have issues with this as well: see
this topic
and
this bug report
.
All in all this looks pretty much like a bug to me... I'm glad removing the Manager group magically made it go away.