This is a tough question, and there is probably no "good" answer for it. The excellent comments posted by Daniel B. and Yannis Rizos are sound, and I'd argue further that the best metrics are those that you understand, along with their causes and consequences.
A recommended lecture for this would be the Goal-Question-Metric paradigm, by V. Basili , further described by L. Westfall . Once you define your own need, then questions, then metrics, and if the CK metrics give you insights on this reduced set, then go for it.
To get back to the initial question (sic;), yes they are still used, even under the wood, as pointed out by Yannis. And for their meaning (complexity, maintainability) I find them relevant — this is clearly an opinion of mine.
As a side note, the CK metrics are first defined in  before being challenged by Subramanyam in .
 V. R. Basili, G. Caldiera, and H. D. Rombach, "The goal question metric approach," Encyclopedia of Software Engineering, vol. 2. Wiley, pp. 528–532, 1994.
 L. Westfall and C. Road, "12 Steps to Useful Software Metrics," Proceedings of the Seventeenth Annual Pacific Northwest Software Quality Conference, vol. 57 Suppl 1, no. May 2006, pp. S40–3, 2005.
 Shyam R. Chidamber and Chris F. Kemerer, "A Metrics Suite for Object Oriented Design," vol. 315, no. December. 1993.
 R. Subramanyam and M. S. Krishnan, "Empirical Analysis of CK Metrics for Object-Oriented Design Complexity: Implications for Software Defects," vol. 29, no. 4, pp. 297–310, 2003.