On allpics.bml page and /data/userpics, those pages will always hit the database and never use memcache. The picture URL field is seemingly never used,and when there are no URLs the value in the memcache key upicurl:$userid will be '', which is false, so the database will always be hit.
This will also happen for any user (without comments on *any* of their userpics) that has an entry or comment on an S2-styled page. No comments on any userpic will make the upiccom:$userid value be '', and will cause the database to always get hit.
The code should use if ( defined( $comminfo ) ) on 309 and if ( defined ( $urlinfo ) ) on 331
Patch available at http://www.pastey.net/109369-3ctc for however long that service keeps pastes. Batteries not included. Content may settle during shipment. Keep out of reach of children. Not responsible for any damage. Some assembly required. Etc.