memcached-tags alternatives?

[Jim Spath]

We're using memcached-tags for an application and have started to 
experience some problems with it as our datasets have grown.  Things 
like losing the tag -> key associations, which is the whole point of 
using tags.

I was wondering if anyone else out there is using memcached-tags and has 
experienced these problems and found any solutions?

I was also wondering if anyone needed tagging support and ended up using 
a different storage engine (e.g. mongodb, couchdb, tokyo cabinet, etc) 
and if it met their needs.

We actually implemented our own tagging solution using memcachedb for 
tag storage and memcached for key storage, but found it to be too slow 
to be feasible.

Thanks!
Jim