Well it's the super's destroy function that sets this.element to null, so in your example above, you will always be doing:
- this.element = $(null);
But is that a memory leak or does "this" get cleaned up too?
My guess is that it might be causing a leak as the super's destroy sets this.element to null and then you set it to an empty jQuery set.
I'd be interested to hear Bitovi's stance on this topic...