It appears that the only difference is:
Z5 has one more mexapixel.
Z5 has larger LCd (2.0 inches).
Z5 is about $100 more.

Amazon shows a ship date of March 25 for the Z5.

The Z3 has enough features to keep you busy for a long time"

If you like action shots:
It has a large variety of "burst" modes.
One will let you take capture 15 1280x940 photos at 10 shots per second.
Another will let you capture 5 2272x1704 photos at 2.5 shots per second.
There are several other modes.

If you want to delve into macro photography:
It has two macro modes.

Why not download the Users Manual and read through it to find out about all of the features:

http://kmpi.konicaminolta.us/eprise/main/kmpi/content/cam/cam_product_pages/DiMAGE_Z3?mDetail=Manuals

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