I believe the OP is talking specifically about Apple products. Because of their popularity and scarcity of official "imports", there are reports in recent weeks that Chinese officials have been imposing duties on the many iPads and iPhone4s that people take from Hong Kong into China in mass quantities for reselling.

I doubt it should be an issue if you're bringing no more than one iPad and no more than one iPhone4 for personal use. And no reports of issues with MacBooks.