I just heard about CDB a couple of months ago and became enamoured with it's simplicity. For applications where updates are infrequent and the size of the database is relatively small (such that the entire database can be rewritten whenever and update is made), then CDB probably cannot be beat for reliability and performance. At first, I assumed that almost no domains would be suitable for this, but I was surprised when I started looking at what I've written that actually is suitable for CDB.
The reliability of CDB depends on renaming a new file over the old database file, and I'm not sure if DJB's CDB calls fsync() or not. tinycdb does not. Make sure your filesystem can't lose your data with a rename before choosing CDB for reliability.