I've got a few shots that I took with my dads D100 in Highest JPEG quality which are printed on fine art paper at 21" by 14" and hung on my wall and they look quite good (only quite good as the printer that they were printed on isn't very good in comparison to the ones I use now). I have also printed several other images on canvas that were shot in RAW with my D100 that are larger in size than those and they look great, as well as a few at 15" square canvas prints which look fantastic stretched up and hanging on the wall. I've also printed a RAW file off a workmates D70 at 30" by 20" and they quality was excellent, she was very happy with it too!
We also did a few (non-scientific!) tests a while ago, comparing the JPEG, TIFF and RAW files produced by the D100 and how well they would come out printed large, and although all produced pleasing results, the RAW files were noticeably better, so I'd defiantly recommends shooting in RAW to get the best quality when printing large!
