In reply to happy_c: I've had lots of back/neck problems over the past few years (in my family too!) and I've found that Pilates is the only thing that keeps my core and outer back strong. I've tried yoga but found you really need a proper teacher that will teach you which poses are okay for you, as many can be injurous to a dodgy spine (maybe okay if it's just muscular though)
I find that when I stop doing regular Pilates, my spine goes all to pot.
I also visit my Chiropracter every now and again and he helps stop segments of my spine locking up and prevents a lot of muscle spasm.