Should I sell my Nikon D90 and get the D5100?

Is their a considerable difference in image quality? I do like that the D5100 is smaller and lighter. I do not have any older lenses, so the D90 internal auto-focus motor is not a factor. What factors am I missing and would this be an upgrade?

In image quality it's only a minor upgrade and only really noticeable on high iso shots. You'd gain a smaller camera, much better video. You'd lose CLS commander, a better control button layout and, indeed, the in-body motor.

Only you can make the choice.

Of course not, if you like the D5100 then get it, but to me I like the D90 better and I still have one, it has features that the D5100 doesn't have, and also the D5100 have features that D90 doesn't have, but the D90 features is more important than the D5100, you need them more, if you want to be a photographer, stay with D90, or at least get the D7000 instead.

If it's video you're interested, then you do have some distinct benefits to gain from the D5100. Otherwise the D5100 would be a DOWNGRADE.

The D90 is a superior camera to the D5100, so it is not an upgrade. The minor differences in the sensors are not significant.

Rumor has it that Nikon will be coming out with 3 more new DSLRs this year, to replace the D300s, D7000, and D3100. Since Nikon has just released the new D4 and D800, the new cameras will make the D5100 the oldest Nikon DSLR in production.

If you want to replace your D90, wait about 6 months.

NO It is not an upgrade

When a person upgrades a camera like the D90, the buy the replacement, the D7000.

They do not move from a semi-pro camera to an entry level camera like the D5100.

As others have stated, the D90 is a semi-pro camera, and an excellent one indeed. It is a benchmark camera that has or will be granted "camera classic status" by Nikonians, and quite likely by the wider DSLR community as well.

The very fact that you are asking this question -- and notably upsetting these dyed in the wool Nikonians -- means that you are probably not using the D90 to the fullest extent of it's capabilities.

To answer your question: It depends on how important the "smaller and lighter" factor is. [You did not mention the flip-out screen or newer-gen video of the D5100, so I'll assume the video of the D90 is adequate for you.]

If the small & light factor outweighs the semi-pro build/ergonomic/handling-speed features, then yes you might want the D5100 instead. [I myself wish Nikon would build a "D400L" alongside the soon to come D400, which would be as small and light as possible, kind of what the Olympus OM series was to the world of 35mm SLR's a few decades back.]

But otherwise, it's basically a downgrade in overall camera quality.

You could always buy the D5100, which is a very good camera, shoot with both for awhile, and then sell the camera that you use less, on eBay.

I happened to be reading Ken Rockwell's site yesterday and he prefers the D5100 over the D90. He says the many of the internal goodies in the D5100 are the same as the D90. That's just his opinion though.Me? I'd like to upgrade from my D40 and I'd like to get the D5100. I know D90s are great cameras and I'd take one in a heartbeat (if the price was right), but they aren't exactly spring chickens anymore as far as DSLRs go. Since you already have the D90, you probably wouldn't be gaining that much other than the better video. But I figure if you really shoot that much video, then you need to get a true video camera.