Out of curiosity, I have been starting my search for a cost-effective backup recently to go with my Nikon D90. I suggested a used Nikon D200 at around $600 a few weeks back, and have totally dismissed the fact I can properly get myself a Canon G10 or Nikon P6000 for that price range.
But with the recent price drop for the Nikon D40, could this mean a change of heart or should I check out the Nikon D5000 at $750 (body only)? Essentially, Nikon has removed the VGA LCD screen, wireless flash commander mode, vertical grip compatibility, lower shoot battery capacity and cheaper body construction from the Nikon D90 to give you the Nikon D5000. But at that price point, its not decisively positioned.
In all, I don't shoot to earn my daily bread, so its not entirely that important if the Nikon D90 should fail on my next overseas trip. I consider this - Good to have.