I think the physical size of the 800 is pretty much perfect, and I prefer it over the larger 900, but the 800 has a few feature shortcomings that make me hesitant.
I definitely find the lack of a forward facing camera on the 800 to be strange. The 710 has one, the 900 has one, but it's missing on the 800 ?
Last time I bought Nokia (my current phone) was a long time ago, because the thing has proven to be almost indestructable. I was hesitant then about a few missing features, but went ahead. No sooner did I, and Nokia released an incremental update that addressed every one of my concerns... Doh!