Some time ago I have tried shooting photos of lightnings with my Canon camera using Motion Detection feature of the CHDK firmware enhancement. Unfortunately without a great success because my camera was not fast enough or software build I've used was not optimized.

But what about n900? Would it be possible to capture a lightning with it our use it as a remote trigger for a dSLR using IR?

Depending on a storm, a discharge may last up to several hundreds milliseconds because of re-strikes, but a real chances of capturing one are when a camera has a response time below 100-120ms. Do you think such response time might be achievable to trigger the back camera?

As for triggering a dSLR, there is already a shutter lag of about 60-70ms (Nikon D90) so would it be possible to have 30-50ms response time with front camera detection (less data to handle?) an IR port?

Unfortunately I'm not a developer nor the n900 owner (yet) but maybe my post will inspire someone to try playing around with that idea. There is software for triggering dSLRs remotely and I think Motion software was compiled on n800.