I've upgraded my SLR from the D3000 to the D90. Since selling my D3000, I've realized how attached I was to my SLR. While camera-less for that week I used my other 4 compact cameras and rekindled a spark for them as well, which is a good thing.
I just got my package in the mail today. I stalked my Amazon.com tracking number until I heard the UPS man knock on the door. The first photo out of the box was incredible.
I upgraded because the D3000 (an entry level DSLR) wasn't as advanced in specs technically as I would prefer a camera to be at this level. The ISO performance was very shaky and didn't give me the results I wanted. The D3000 isn't compatible with all Nikon lenses and it does not receive wireless communication with accessories such as an external flash or a remote. Rather than going just a step up and getting the D5000, I wanted a DX body and opted for the D90.