Agreeing with Jan (and myself) - too much overhead to check for 
something that really isn't broken in the first place.

What if the textarea has a single space in it?  It will look blank to 
the user, but spellcheck would be enabled.  It might confuse them why 
spellcheck is enabled in this situation, but be disabled in a 
situation (truly blank message) that may not be discernable to them.



Adding a bunch of javascript to check for this (it may be trivial in 
the text case, but it may require quite a bit more for html mode) 
doesn't seem to be worth it IMHO.

I'm confused. Why do you want to be able to spellcheck empty text?

You don't, but it doesn't matter if you do. It adds a needless check, 
smells to me like Windows' "Are you really sure you want to move that 
object to the trash?" kind-of questions.

Right, but why do you need to spellcheck it?

Why? If you send a message without entering text, the recipient will 
get an empty message. So what? I mean, it doesn't break anything or 
doesn't do anything unexpected.

Sounds reasonable to me.

If you click "check spelling" on an empty message the textarea turns 
to a blank area.  Should the spell-check button just be disabled until 
text is actually entered?