I kept my old bodies until I had three DSLRs sitting around, which was just more than I needed. So I sold the first to a friend (her first SLR), which'll let me keep an eye on it to make sure it's well-treated, and introduce someone to a new hobby at the same time.
The middle camera was originally my backup, now it's sorta that and sorta the wife's DSLR.
I have no plans on upgrading, and the only thing that I really wouldn't mind in the body is even better AF - it can never be good enough, when shooting in Haunted Mansion or similar.

It would actually be interesting to try a D300/40D on a dark ride to see how it compares - I suspect it's pretty close though not
quite there. But other than that... I doubt low-light ISO on an APS sensor will get much better for a little while, I certainly don't need more megapixels, and I don't care about faster continuous shooting.
While mentioned megapixels -I gotta say, as one of the "mp don't matter" crowd, I'm almost convinced now. 14.6 megapixels means that viewing photos at 100% reveals an
astonishing amount of picture data - I almost wish I could most my Illuminations shot that I just processed at full size, there's lots of things lost when shrunk down (like seeing the actual people on the other side of the lagoon!) I am definitely glad to have all that picture data.
Rumor is that Pentax and/or Samsung is working on a full-frame DSLR soon, and no doubt my camera will be replaced with an even more advanced one before too long, but for now, I'm happy. I'm also not particularly inclined to go the full-frame route at this point. The prices are nuts, the cameras are quite big and heavy, and the main advantages IMHO are wide-angle shooting, though low-light is certainly a point in the D3's favor, but were I a Nikon shooter, I'd still go for the D300 over the D3.