Problems updating my Debian Distribution, or do you know MMAP?

I was recently trying to update my Debian (lenny/sid) distro and ran into some problems I never had so far:
When calling

apt-get update

I got the following error message:

E: Dynamic MMap ran out of room
E: Ein Fehler trat beim Bearbeiten von g++-4.2 auf (NewVersion1)
E: Problem with MergeList /var/lib/dpkg/status

After digging around I found a solution for my problem:
Increase the Cache Limit size of APT in /etc/apt/apt.conf like this:

APT::Cache-Limit 80000000;

Be careful not to set the size too high!