Well, I'm still having problems with the seven second delay. However, I've tweaked the script to include dbus commands for turning on and off the status led (which also seems to have some timing issues), and added it to my menu, so I can set up my N900, open the lens and adjust the focus, then close the camera app and tap on the hdr app to get five photos.

I've written a little bit about it in my blog post High Dynamic Range (HDR) Imaging on the #n900 Using Gstreamer and Enfuse which I hope to expand upon further. It does seem like with a few of these pieces in place, building an app should be pretty simple.