I am with you on leaning toward the Sony P73.
I have concerns about the picture quality of the Casio.
Here is a side-by-side look at the specifications:
http://www.dpreview.com/reviews/compare_post.asp?method=sidebyside&cameras=casio_exz40%2Coly_d580z%2Csony_dscp73&show=all
....
Hi, I am looking to buy a digital camera - this is my first time. I want 4.0 megapixels based on my needs and have done alot of research. I basically narrowed it down to 2 choices - the sony cybershot dsc-p73 or the olympus d580. i was leaning more toward the sony one when i spoke to somone who used to be a salesman at b&h and knows his stuff. he suggested i get the casio ex -z40. now i am confused - can anyone give me advice? thank you .

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