If you prune H. macrophylla's at this time of the year, you will be removing flower buds, since they bloom on last years growth(old wood). I would wait until new growth appears in the spring and then remove any dead canes or branches. If you want to shape them up, wait until they have finished blooming in the summer(assuming they do bloom) and then remove up to one-third of the canes. If they are overcrowded in the center, that would be a good place to start, to allow good air circulation, which helps to prevent powdery mildew.
Rb

I'd add that your friend was mistaken about the variegated hydrangea as well. As it is a macrophylla also, cutting it back to the ground each season removes any possibility for flowering. A number of folks find variegated hydrangeas less inclined to bloom, but they do and profusely, specially in a benign climate like yours. See the recent "variegated hydrangea" thread for a glimpse of how lovely these plants are in bloom and put your pruners away :-))

I experimented with Lady in Red last yr in my zone 5 yard. With loads of winter mulch, it made it through the winter and it's full of the beginnings of new growth now. My question is whether or not I should take a stab at transplanting it to a new location. Any ideas?