Gnutellafan, rehashing doesn't work if you do not have the full content. So any bad/broken client can send junk data, you won't recognize until you downloaded all partials. A SHA1 hash does really give no security on resume time, a simple overlapped check does this allready.
So while HUGE favours SHA1, I think it's a unnessecary waste of bandwith and therfore I personally don't support this idea, I prefer other alternatives. The GDF can vote a lot of things... I think discussing ideas, improving design, understanding background details, find better alternatives for the next protocoll is still allowed in this place.