Hmm, actually trying to do something more complicated than I had thought. The export option from photoshop works nicely (Scripts->Export Layers to Files...) With Gimp I've placed the script in the Gimp_2.6 scripts directory, refreshed the scripts and restarted it, but I can't find where the command turns up. It should be under File, but I don't see it...

The secondary issue is that I'm trying to do the following:

Save out the different layers as pngs. Import them into an iPhone app and rebuild the layers there (after editing the colour on one of the layers). The problem I have run into is that Gimp's overlay blend layer doesn't seem to be a proper overlay. This means that I can't reproduce my image from the layers in photoshop (which has the same blend modes as the iPhone). From a little reading it does seem to be the case that Photoshop doesn't have a parallel for Gimp's overlay. This raises the slightly distressing possibility of having to rerender quite a few images in photoshop that I thought I already had nailed down in Gimp.... Any thoughts?

Thanks everyone already for your help. Very much appreciated.