Compared to...

Studio scene comparison (higher sensitivities)

The E-510's default Noise Filter setting keeps visible noise to an absolute minimum at the expense of image detail which is frankly heavily blurred. As you'll see later in the review if you're not uncomfortable with a little visible noise you can turn the Noise Filter setting off (and turn down sharpness) to get the more detail.

ISO 800

Olympus E-510 Olympus E-510 (Noise Filter Off, Shp -2)
Sony Alpha 100 Canon EOS 400D
 
Pentax K10D  

ISO 1600

Olympus E-510 Olympus E-510 (Noise Filter Off, Shp -2)
Sony Alpha 100 Canon EOS 400D
 
Pentax K10D