Using the standard pinboard as supplied with RISC OS does present some problems for MoreDesk - it isn't very fast at dealing with being updated on desktop changes.
On an Iyonix, performance is generally pretty good all round. On VirtualRPC it isn't bad but on a StrongARM RISC PC it can feel a little slow. This program hasn't been tested on hardware older than that.
The first step to improving performance is to use a tiled sprite as your backdrop image, rather than a JPEG. This can result in a significant improvement in the speed of switching desktops.
Pinboard association (as opposed to backdrop image association) is quite expensive for desktop switching time. I suspect this is because the Pinboard is checking every pin icon against the associated object on the hard disc when it is added, which slows things down quite a bit. It also seems to be related to how the pinboard window appears to be redrawn in lots of little rectangles (one per pin icon) rather than all at once.
Because the Pinboard wasn't really designed for this, it doesn't bother caching information or making the reloading of a set of pinboard icons particularly fast.
If this is a real problem on your system, the only option is to disable pinboard association in the MoreDesk choices.
The main desk space view should quickly on all systems, but you can boost performance of that a little by switching off the “task sprites” option in the MoreDesk choices.