In my case its not doing the tasks slowly, but its slow to start them, taking a lot longer than usual to pick up changes in a folder on Mavericks 10.9.5/Hazel 3.3.2.
In the photo import folder, it used to start almost as soon as the images started coming in in the couple of months I've been using it, but now its taking 5-10 minutes to start, and a similar amount on a subsequent folder the images are moved to.
I can't tell with other actions, because the photo import are the only 'real time' rules, so I just wouldn't notice.