The Tampa Tribune has an article looking at various issues on which presidential candidate John McCain has, in effect, punted, citing states' rights. These include offshore drilling, abortion, adoption by same-sex couples and the teaching of intelligent design.
The article quotes some talking heads as saying it's a way of evading a question, plus one who says McCain has been pretty consistent in citing federalism concerns.
As someone who has written a fair amount about federalism, I would say that states' rights tend to be less of a priority than the political points that can be scored by going against them on a particular issue. There are so few exceptions among members of Congress in terms of people consistently upholding states' rights that it's unusual, and therefore striking, that McCain express consistent concern about them.