The only love-hate I can think of is roses. Just when I think they are not worth the trouble, they bloom and all is forgiven. I'm good with goutweed, it's not too much of a bully for me and is a useful ground cover. I just plain don't like the smell of houttynia, but haven't found it overly aggressive. It's in a hosta bed that is rather separated from my other gardens so perhaps that's why it has not been a problem. I guess borage might be another love-hate plant, heavy on the love side. I love the plant and that it reseeds itself but have to continually remind myself to only allow one every 10' or so. It makes a lovely blue accent just about anywhere it lands.
I could certainly add to a hate-hate thread...
