My load script keeps dying while doing a geonames lookup, but almost every time it's when it's doing a lookup with a latitude of 180.0 degrees or -180.0 degrees. The geonames lookup either gets a socket time-out or returns a 503 error. It doesn't seem to happen when doing lookups with different longitudes.
I removed any code related to geonames from http://www.ratethisplanet.com, thinking that it could cause problems, but it probably wasn't. Thing is, PHP's curl_init() does seem to consume a lot of CPU power.