I am a D3100 owner too, it is my very first DSLR, which was bought in July last year.
Prior I have 2 Minolta SLR, the oldest was bought in 1994 but broke down and the second one was sold away
to make room for the D3100.
I am relatively happy with the camera except
1) It does not have Fv Lock (Flash Exposure Lock)
2) It does not have Focal Plane Flash ( meaning low flash sync speed at 1/200th max)
3) It does not have flash commander mode. (meaning no iTTL for my SB700 when it is away from camera hotshoe)
For 3) I have to use my flash meter to replace the loss of iTTL and use my flash and camera in M mode. Not forgetting the flash triggers, without them it won't work.
Not very convenient.
I am new to DSLR but I know D7000 have all the 3. It is very attractive to me. haha