Same problem here upgrade from 2.0.7 to wp2.1
The server is running PHP 4.3.10-18 and Apache/2.0.54
i get tons of:
(32)Broken pipe: core_output_filter: writing data to the network
child pid 3943 exit signal Segmentation fault (11)
the website is only rendered partially.
strange fact: this is the only wp 2.1 on my server that keeps on crashing. all other instances run fine