Anyway, other than what was mention, the main thing was that TS had to look into the following,
1) Size and weigh
2) features - vari-angle LCD, great movie mode, in-build motor
3) form factor/ ergonomic (grip design, button and dial's layout, etc).
D5100 is a newer camera as oppose to D90, although was consider as an entry-level camera, it produces very very good images, the lack of inbody motor might be a deal breaker for some, but seriously if TS already have this camera, maybe he/she should try out manual focusing and play around with it till he/she could save up enough for a D7000 or D700 (D800).