One is not allowed to take God's name in vain, and certainly not allowed to curse the name of God (chas v'shalom). I'd like to understand conceptually why these things are considered such grievous sins. Why is misusing God's name so bad?
With regard to taking God's name in vain, the Chinuch (Mitzva 30) goes into great detail why it's forbidden, but basically
1) swearing unnecessarily in God's name shows that you have no respect or fear for the Master of the universe (and all the other attributes the Names of God encompass)
2) swearing falsely in God's name is forbidden because God is Emes and by doing that you imply that something related to God can be false chas v'shalom
edit: Hey turns out I have the volume of Artscroll Sefer Hachinuch that covers "blessing" God as well:
Says the Chinuch (Mitzvah 70),
Both this and Mitzvah 69 (the prohibition to curse a judge) are derived from Shemos 22:27, אֱלֹהִים לֹא תְקַלֵּל.