If Nikon brought out a body with a full frame sensor and a few more MP than my D90 for around 1000GBP and sod the fun features I might be tempted to upgrade. As it is, all the recent new models seem to be aimed at new buyers, not one of them has anything that would compel an existing user to upgrade. I avoid DX lenses just for the day when I can afford such a body. I live in hope that the rumoured D800 comes in well below the prices that are being put around.
As for the D5100, yes. it seems to be nice camera but I won't be rushing out to buy one. Oh, the trash button is in a rather exposed place.