Your metering mode also matters.
Whther you lock exposure values when u recompose also matters.
Setting exposure compensation also matters.
There are alot of factors, in any case, no camera will give you the perfect exposure, u have to decide urself. I am using d90 too, read reviews that its metering tend to overexpose, but so far no issues for me.
There's only inaccurate shutter speeds btw. Unless ur shutter is sticky, which is unlikely.