I wrote a plugin to fix this issue:
2 2013-01-01 08:11
Topic: [Release] CloudFlare (2 replies, posted in PunBB 1.3 extensions)
CloudFlare v0.5.0
Integrates your PunBB with the CloudFlare CDN.
This will override the detected client IP with the CloudFlare HTTP Header HTTP_CF_CONNECTING_IP if detected. Clients that bypass the CloudFlare CDN will still show thier correct IP.
Tested with 1.3.4 and 1.4.2
http://troy.sh/downloads/cdn_cloudflare-0.5.0.tar.gz
HTTP Header and IP detection code borrowed from CloudFlare Wordpress plugin. If there is interest I could look into porting over the Spam submission code to automatically publish spam information out to CloudFlare.