I'll bet that if you're not adding a ton of records you might be ok with GDBM. Even if the db is locked for reading, (does anyone know if GDBM does this?) the access is quick enough that even under the kind of load you're talking about you'll probably still be ok.
However, I have recently (in the past few months) graduated to using DBI and mySQL and I have to say that the learning curve really isn't that steep and the "real" dbs make lots of things much easier to do than the tied hash dbs. I always hated rolling my own routines to split and join records to do inserts and updates. So much easier in mySQL. If you have mySQL (or similar) available to you you won't regret moving your project over... and you'll probably get to trim alot of your code in the process.
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