For me, a simplicial groupoid is a simplicial object in ${\mathbf{Grpd}}$. I am more general than Goerss-Jardine in this definition.


Do you have examples simplicial groupoids that occur in nature? Here's what I have got:


1. Given a simplicial group $G$ acting on a simplicial set $X$, the action groupoid $X//G$ is a simplicial groupoid.
2. The fundamental groupoid $\Pi X$ of a bisimplicial set or simplicial space.
3. Given a functor $F:I\to {\mathbf{sSet}}$ from a diagram category $I$ to the category of simplicial sets, one can form what Goerss-Jardine calls the translation category $E\_I F$ and what Mac Lane-Moerdijk calls the category of elements $\int\_{I^{\mathrm{op}}}\, F$. The nerve of this category calculates the homotopy colimit ${\mathrm{hocolim}}\_I \, F$. 
In the case where the diagram category is a groupoid, then this translation category/category of element is a simplicial groupoid.
4. Given a simplicial set $X$, the loop groupoid $GX$ is a simplicial groupoid.



Examples of Simplicial Groupoids in Nature
See some papers following 


Ehlers, P.J. and Porter, T. Varieties of simplicial groupoids. I. Crossed
 complexes. *J. Pure Appl. Algebra* 120~(3) (1997) 221--233.


(which you may already have). 


As another example, given a double groupoid, it's simplicial nerve in one direction is a simplicial groupoid in your sense. There are *lots* of examples of double groupoids, see for example my arXiv paper 0903.2627. 


