"Praise you" is not an imperative, it's present tense. It's like saying "We/I are praising you." Imperatives can't have a 2nd person as the object, they need to have a 3rd person object ("Praise him!"). And praise always needs a subject, I think. I can't think of any examples where you could use praise without an object. http://www.italki.com/teacher/T005650036.htm To respond to nanren888: "Bite me" literally means "you bite me," which would be an imperative, so you're right, there can be a 1st person object.

"Praise you" is an imperative. Old fashioned and usually used in the bible.

Your question needs more context to answer properly. . Amy's answer is I think a little misleading. "Bite me" seems pretty imperative to me, & seems to have a first person object, so I suspect what Amy says about objects in particular persons is inaccurate at best. "Praise be" is an old expression & therefore probably acceptable English.