Mercifully, I don't. Yes, on Idea once in several days/weeks a stray SMS does come in, but I promptly lodge a complaint with Idea for it, and they inform me about the action taken after few weeks.
With RGSM, I recally getting only 1 SMS after registering with DND (more than 6 months ago).
With Docomo, I haven't bothered to register with DND as they send just about 1 promo SMS a day and calls are even lesser. The issue with DND is that they (all operators, AFAIK) even stop sending useful offers. So in Docomo's case, I haven't registered.