They are priced about the same and their specifications are very close.

The S70 has a wide angle lens - good for indoor photos of groups. And it uses lower cost Compact Flash cards as opposed to xD cards for the P810.

The P810 has a larger LCD and the ISO goes to 800.

Now, to make it harder --- take a look at the Fujifilm E550. It was introduce the same time as the P810 and it has almost exactly the same specifications. It appears to be a cost reduced P810, probably to cover a different price range. It cost about $100 less than the S70 or P810.

Here is a link to a side-by-side comparison:

http://www.dpreview.com/reviews/compare_post.asp?method=sidebyside&cameras=canon_s70%2Cfuji_finepixf810z%2Cfuji_finepixe550z&show=all

And here is a review of the Fujifilm E550:

http://www.dpreview.com/reviews/fujifilme550/

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