Hello rio!
12 Mp and 24x optical zoom sounds good on paper but ... reality strikes back.
Nikon P90 1x optical zoom:
http://www.cyberphoto.se/bildexempel/p90/DSCN0003.JPG
Panasonic FZ28 1x optical zoom:
http://www.cyberphoto.se/bildexempel/fz28/P1000027.JPG
Nikon P90 24x Optical zoom:
http://www.cyberphoto.se/bildexempel/p90/DSCN0006.JPG
Panasonic FZ28 18x optical zoom:
http://www.cyberphoto.se/bildexempel/fz28/P1000025.JPG
The Panasonic FZ28 lens is better, producing sharper images with less chromatic aberration. Nikon P90 pictures are - to my eyes - noisy and undetailed considering it's a 12Mp camera. From what I've read, Nikon P90 can only record video in VGA and optical zoom can't be used when recording. Nikon P90 ISO 800 (and beyond) performance isn't very good.
Nikon P90 ISO 800:
http://www.cyberphoto.se/bildexempel/p90/DSCN0027.JPG
Panasonic FZ28 ISO 800:
http://www.cyberphoto.se/bildexempel/fz28/P1000037.JPG
I would recommend the Panasonic FZ28 over Nikon P90 based on these pictures. I love the Panasonic FZ28, it's a great camera. So is Canon SX10 IS.
Hopefully Gordon Laing will be able to review the P90 and the 26x optical zoom OLYMPUS SP-590 UZ soon enough.
Edit: Correction!