The last line of /etc/default/tomcat6 on some machines (at least imlczo) is:
JAVA_OPTS=" -Dorg.apache.tomcat.util.buf.UDecoder.ALLOW_ENCODED_SLASH=true"
which overwrites the earlier JAVA_OPTS line with the -Xmx flag to set the heap size and the change in garbage collector.
Both sead and nced already have fixed versions:
JAVA_OPTS='"${JAVA_OPTS} -D ...

which should be propagated to all machines (and the VM download?) to put the new -Xmx1g heap size into effect

sead also has three additional lines:

1. Path to native libraries
   JAVA_OPTS="${JAVA_OPTS} -Djava.library.path=/usr/share/tomcat6/lib/amd64"
   GDAL_DATA=/usr/share/gdal/1.9
   LD_LIBRARY_PATH="/usr/lib:$LD_LIBRARY_PATH"

are these useful on the other machines?