There's definitely a line worth not crossing if one does have a plan to do an April Fool's prank, but I see no harm in doing it as long as that line doesn't get crossed. In recent years, it's been the whole "We're pregnant!" announcements on April 1st. Well, firstly, it's played out. Even now, on March 31st, everyone posts on their Facebook saying "Don't believe any pregnancy announcements tomorrow!", and secondly, it can be perceived as insensitive to those who either can't get pregnant, or who have unfortunately experienced failed pregnancies. So I think stuff like that crosses the line.
But...playing harmless pranks on someone for the sake of April Fool's isn't so bad. Like shaving cream on the hand while sleeping - that's just funny.

I guess my standpoint is if you're going to do an April Fool's prank, just don't be mean about it.