I now have 20% or more of the "visits" to my site being hotlinks to images on my site. It's about 2500-3000 a day.
I'm torn between continuing to allow the hotlinks because something in my head says the hotlinks contribute somehow to the site's rankings, or preventing hotlinking completely through a rewrite of some sort.
There are certain times of day when the server slows down momentarily because of the load, so blocking hotlinks would help that. If they have any value for SE ranking, though, I'd rather find another solution to the server issues.