i'm using the stock php3.ini file.

compile time options:
./configure  --with-apache=../apache_1.3.11 --with-mysql=/usr/local/mysql --enable-debug=no --enable-track-vars=yes --enable-bcmath=yes --enable-memory-limit=yes --with-imap --with-gd=/usr/local/include/gd

When using preg_match_all (in place of preg_match) like this:

$thing = "blah@blah.com";
if ((preg_match_all("/\@/i", $thing)) && (preg_match_all("/\./i", $thing))) {
  echo "match";
}
else { echo "no match"; }

hitting it with a web browser causes a segmentation fault (11) error in the Apache (1.3.11) logs:
[Wed Feb 23 19:31:46 2000] [notice] child pid 20345 exit signal Segmentation Fault (11)
and the page comes back as having No Data.
it doesn't kill the webserver or cause any further problems (except causing IE to run slow until it's restarted :P )

The error and problem are completely reproducable.

Unfortunately, i have not been able to test this with the most recent version of php (for which i apologize for posting this anyway), but it broke some obscure parts of a set of live scripts i have and had to revert temporarily :P