Dumping Cache is a feature that is discussed in details. I agree that dumping cache to keep it warm may not be the best idea. However, I recently got into the situation where we lost the database and we lost the backup of the database. So, the only thing we had was running memcached (please stop laughing, it's only a little funny)... So I had to dump the content of memcached to attempt to recreate the data....
I used the tool described here: http://lists.danga.com/pipermail/memcached/2007-April/003905.html But the dump was painful as I had to dump chunks and then delete them from memcached so that I can dump other chunks. Is the feature to dump cache still being considered? Thx! ~.b