If you are a Window user and are using or want to use R and GRASS in combination, you will be happy to by this announcement on the GFOSS blog that there is now a better integration of WinGRASS 7 and R.
This integration is available for Linux users for a very long time. It was actually one of the principle reasons I started to use Linux. But now Window users can enjoy the experience too . Further user instructions are given on the GRASS wiki.