I just started using ABS myself (white pvc before). I really like the black much better. I don't see why it would'nt hold up indefinately, since its designed to move water.
I considered painting the pvc but was worried about flaking over time. I've got a petsmart polyresin root thing thats lost all its paint
What I'd really like to try is coating some pieces in gravel or sand using silicone....just have'nt gotten serious about it.