John,
I know you're in the U.K., but at Pointivity (U.S. based) we host Dynamics GP for Microsoft System Integrators and ISVs. We are not a system integrator ourselves but a dedicated application hosting company. We have had much success working directly with system integrators and Microsoft Partners to host Microsoft Dynamics GP, Dynamics CRM, Dynamics SL, and other related products such as SharePoint, MS Excel, FRx, etc. in a hosted environment using terminal services and Microsoft's SPLA licensing program in a SaaS model. SPLA licensing program allows you to licensing Dynamics GP on a per user, per month basis with no large up-front licensing fee or capital expenditure for the servers and server setup/maintenaince.
If you have any questions about Dynamics GP in a SaaS format I'll be glad to help you. You can learn more about Dynamics GP SaaS offering at http://gp-spla.com.
PS - we host Dynamics GP and related products for companies all over the world. Companies today often have accounting and sales forces outside of the country and we come across the need for this type of solution on a regular basis.
Thanks,
Derek Cahill
VP Channel Management
Pointivity (a Microsoft Gold Partner for Advanced Infrastructure Solutions)