Some of the template meta programming stuff he gets into isn't very portable and is very hard to debug when things go wrong. My rule of thumb is if I think I need to implement something from Modern C++ Design I am probably better off thinking about the problem a bit more and doing something else instead. Since it's been a while since I last looked at it I'd guess that some of the portability issues have gone away as compilers implement new features.
The implementations are very different. The implementations in Modern C++ Design used a lot of tricks to work around features the language didn't have. This isn't an issue when those features are part of the language. I'd also point out that even now there are parts of the newer standards that aren't fully supported by all compilers. Something being part of the standard doesn't mean you can use it on every platform.
Advanced, sure. But dangerous? I've never heard that. Do you have any specifics?