It can be terrible.
Do you use straight quotes or curly quotes?
If you use curly quotes, OO adds one word for every pair.
ie. "I went to the shop." would be 6 words.
It's better with the straight quotes, but is still glitchy on other things like dashes (apparently, I'm not a big dash user).
Which is sad, because I really like OO. (Plus, I really don't feel like paying for MS Office. )
I use straight quotes, which minimize that. But in regard of the em dashes, oh God. No wonder Clarkesworld said it was too short, because I had nearly twenty em dashes!
*Shakes head.
Thanks for the info, though, Lillie.