I still think it's a good habit to get into. In fact, I know it is. C++ is all about systems programming, so eventually you'll get into compiler design, interpreters, device drivers, operating systems, editors, file utilities, and performance executives that will need the register keyword. Think outside of MS's compilers. There's a whole different world out there where you shouldn't second-guess each compiler (and there's tons of older ones you'll need to use eventually). If it ignores the register keyword, big deal. At least you sent a request, and that's better than not doing so. That's why it's a good habit to get into - it's good practice, and it shows that you care about a possible performance boost, or some special treatment from the compiler.
This is Microsoft specific if you have Visual C++:
The compiler does not accept user requests for register variables; instead, it makes its own register choices when global register-allocation optimization (/Oe option) is on. However, all other semantics associated with the register keyword are honored.