502 = bad gateway (php-fpm problems, etc.)
Does googlebot consider them 503? (503 = server overloaded & try again later)
google supports HTTP 502
http://www.google.com/support/webmasters/bin/answer.py?answer=40132
and treats them as
502 (Bad gateway)
The server was acting as a gateway or proxy and received an invalid
response from the upstream server.
in my experience google treats 502 as downtime and stops hammering your server for some (short) time.