It seems that having a main or 'core' style of martial arts is crucial to making cross training beneficial. Some styles incorporate cross training right from the start, which is great, as long as it's done properly and doesn't conflict with the core teachings.
J.C. made a great point over at Bujutsu: The Path, entitled Cross thinking.
The point that really hit home was that the very act of blogging, reading, and researching martial arts, we are, in fact, doing a form of cross training. By having an open mind, we are opening ourselves up to potential improvements in our training.
I've made comments on other people's blogs, I've agreed and disagreed with points, and readers have done the same on mine. I've enjoyed the different perspectives, and sometimes, I've changed or adjusted my opinions on matters. Looking at things from a different viewpoint has helped me in my own training.
So bravo to J.C. for pointing out that Cross thinking is actually a form of Cross training.