was very happy to read this, since I've had the same problem at times. I've found that the black teas can be a bit bitter, but taste great after an initial infusion. So, sometimes I just do a quick "wash" (let my leaves steep for 2 minutes or so - dump it - and reinfuse the suggested 5 minutes), or I use less leaves. I guess this is what Chris meant by bitterness being an issue of both "time and volume." Tihs doesn't seem to the be case with herbals and white teas (actually, that's not true - the Silver Needle is susceptible to bitterness), but oolongs, greens, and blacks can indeed become bitter.
I hope this info helps some with a similar problem.