# aptitude install zend-framework
I uncommented the line with the include path to make it usable:
# vim /etc/php5/apache2/conf.d/zend-framework.ini
Then restarted Apache. Unfortunately it crashed straight away:
Aug 3 11:42:44 the-lake kernel: apache2: segfault at 0000000000000008 rip 00002b3c755d5070 rsp 00007fff3d94c1c8 error 4
Some searching revealed it was this bug.
Setting an initial
/etc/php5/apache2/php.iniworked around the problem.