Some of the problems on a website are down to the server or the server host provider being stingy with the memory. For a Drupal website for the image handling and other bits you want at least 128m of RAM, but some hosts limit you to much less (1and1 only give you 30m in some cases.

To combat this - and some other issues - we create a php.ini file in the public_html (or other root) folder and add the following:

memory_limit = 256M
safe_mode = off
session.cache_limiter = nocache
open_basedir = none
extension = pdo.so
extension = pdo_mysql.so