It's interesting that it's hard to explain, because the fingers will play the chord by themselves and I need to stop and think to know what I am actually typing.
C-x r k to cut a rectangle, and C-x r t to add one filled with, for example, the comment symbol:
Holy crap, thank you very much! Looks like cua-mode rectangle select might actually be the equal of Visual Studio's very straightforward rectangle selections...
C-x r k to cut a rectangle, and C-x r t to add one filled with, for example, the comment symbol:
(C-space)this
to comment
C-x r t #
#this
#to comment