I have vague recollections that he'd read that Caldera said reiserfs can have problems with file corruption under very heavy load. But I've not been able to find anything to back up that recollection... I didn't see anything on [link|http://www.aaxnet.com|[link|http://www.aaxnet.com|http://www.aaxnet.com]] about reiserfs.
Everything else I've read about it has been amazingly positive. No personal experience though...
Cheers,
Scott.