The most significant thing in the D3100 is autofocus in liveview and movie mode (first in a DSLR). How well it works remains to be seen but its nice to see Nikon moving forwards with video features (including 1080p recording). Overall the package looks very strong for a 700 dollar camera (with kit lens). Highlights include: 14MP sensor and increased high ISO (3200, decent for an entry level camera…again depends how good the pictures are at this setting).
Read Nikon’s blurb: http://www.nikon.com/about/news/2010/0819_d3100_01.htm