i use a d40 with kit lens.
sb-800 is smaller, cheaper, and as powerful, recycles with 5 cells as fast as sb900 4 cell.
only thing whr ppl rate sb900 better is its menu system if your a CLS user, and DX-FX adjustment thing.
ive used sb800 on d70 with kit lens, one could feel sb800 weight. sb900 is even bigger.
flickr.com/aimenrg, urs?