The ERDAS browser client was impressive and easy to use; although Chris does not normally demo this product we were quickly able to figure out what the screens were asking of us and collect "Elevation Change Defection" results back for display.
When we got down to technical details ERDAS had reached the limits of the WPS specification. The WPS DescribeProcess data structure does not supply quite enough information for their user interface needs (example field validation). I hope the future versions of WPS will be more helpful in this regard.
That said they were not limited to their WPS server; and had performed testing with either 52N or deegree (sorry I cannot remember which as they did not have one in their booth to test against).
I also recognised an old friend in the NDVI vegitation model, a classic we had slated for last years WPS shootout.
Aside: Thanks to LISAsoft for sending me to Spatial@Gov it was a fascinating look at the Australian Geospatial scene.