This is definitely not desirable. It is caused by two issues, first the pylon to casting gets loose over time, and second, the bolt holes in the pylon get "rounded" out and enlarged over time. Both will cause flex in the frame, and both are fixable.
The first issue is fixed by "gluing" the pylons into the castings with Epoxy. A lot of people do this to extend the competitive life of an older boat.
The second issue is fixed by restoring the pylon bolt holes and re-drilling them, as in the hotline issue below.
Here is a link to a Hobie Hotline issue addressing both:http://www.w1dm.com/projects/HOTLINE/10-03-04%20HOTLINE.pdf