That looks like pretty classic blossom-end rot. The main Tomatoes forum has a FAQ answer that may help you deal with it. :)

--Alison

Ah, yes. That certainly does seem to fix the blossom-end rot descsription to a T (and also explains the similar plight of some of my squash)! I'm guessing the root cause is more moisture related than anything else - this is the first year I ammended my garden bed and I did use manure in prepping it. I'll turn down my drippers and see what happens..Thanks!