It depends... I generally never tire of the act of photography. Often, if I can get into a groove, it can be quite a rush. A bit of a high. Sometimes I do feel I'm approaching things the same ways and need to somehow mix it up, but tend to fall back into familiar patterns.
Where I feel some burn out, or at least lack of enthusiasm, is dealing with the tasks of image processing (BTW, I'm 100% digital capture, and I definitely produce a lot more due to this). Sometimes I feel like I'm being buried under a mountain of images. 🙂 Yet, I can't stop creating images. I do go periods of non-shooting. Days or a week, perhaps. But at my current age (mid-40s), the feeling of mortality is starting to creep in, along with the thoughts of how much longer I'll be able to go about shooting relatively effortlessly. Therefore, there's a reluctance to scale back.