The D5000 is a pretty good camera, I used it for about a a half a year and it was capable of doing most things needed. The ability to use high ISO is great, the sensor in the d5000 similar to that of more expensive Nikon cameras like the d90 and d300.
But the main downside with the d5000 for me was the ergonomics. If you have the money to go with the Nikon d90 at least consider. They are very similar in IQ, but the d90 has a better feeling build (IMO) dedicated buttons for ISO, WB, etc, a slightly larger view finder, a built in motor, and a few more handy additions.
I think you would enjoy the d5000, especially if this is your first DSLR. But if you're buying it new, the price shouldn't be that far off from a d90 used. Just something to consider.