Thanks for your reply.
I was successful in implementing a solution for the spatial query following your second suggested work around. I used the GetRows(Int32) method, passing an array of ObjectID value, to come up with a unique set of search results. Not very efficient, as the search method is called numerous times, but it works great nonetheless.
I also experimented with suggestion #3, i.e. creating a single geometry object to base the search on, but didnít quite get a satisfying result (close, but not good enough). I would not recommend this option.
Finally I havenít yet had the chance to try the first work around but I can see why youíre suggesting it is the best solution, as ultimately ArcGIS Explorer is designed primarily for consuming services and not so much for doing client-side geoprocessing. I havenít yet tried using the SoapConverter class, but it seems simple enough. However Iíd like to know if the next release of ArcGIS Explorer will provide the ability to add and consume a geoprocessing task without the need for a developer to build an interface specifically for this purpose, just like we were able to do with ArcGIS Explorer 500. Thanks for letting me know if ESRI will provide this functionality.