You guys were apparently right, from the log it seems it was the php memory limit after all. I got plenty of errors similar to the one below (for various plugins):
[Sat Dec 11 00:43:40 2010] [error] [client XX.XXX.XX.XX] PHP Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 798980 bytes) in /home/halibutt/public_html/wp-admin/includes/admin.php on line 40, referer: https://halibutt.pl/wp-admin/edit-comments.php?comment_status=spam
I checked and my host offers only 32M of memory, which is close to peak usage of my site (typically it’s around 29, but apparently it jumps up every now and then. Do you think enlarging it to 64M might solve the White Screen of Death problem once and for all?
Cheers