Yes, they do look very similar. If you do the side-by-side comparison on dpreview, there are few important differences. However, there are a couple. I have the s770 and really like it. I've had it for a number of months now, and would not switch with any other current p&s camera if given the opportunity. In other words, I think it is the best camera for me at present. I had the z850 and liked that a lot too. Search for s770 on this forum to see many posts I and others have put up about it.
The things that stood out for me on side-by-side of the s770 and z70, that would make a difference to me, are these:
1. s770 has 2.8" vx 2.5" lcd. One of the great things about the s770 is the wonderful on-screen panel menu for settings. I much prefer this to the function wheel of the z850. And it is far better to have this kind of right-there menu than to search through levels of menus. I'm not sure what the z70 has, but with a 2.5" lcd, if it has a panel menu, it would get in the way of the picture preview.
2. The s770 has 230,400 lcd pixels vs 115,200. Some of this difference is due to the larger lcd, but even so, it has twice as many pixels, and I'd guess the lcd screen will be better resolution on the s770. One thing I really like is to be able to pop the camera out and show folks pictures on the lcd. With the huge, bright, beautiful s770 lcd, this is lots of fun. Everyone remarks on how clear the pictures are. And, you can set it for various lighting conditions, and enhanced color vs. natural etc. Though you can probably do that with the z70 too.
3. The s770 has MPEG-4 video, and I don't believe the z70 does. This means you can fit a lot more video on a card. I don't do much with video, but it's nice to have the capability if needed.
4. The s770 is noticeably slimmer, at 17mm vs 20mm for the z70. This is a feature I really love about the s770. It rides very nicely in pockets. Though the z850 is pretty small, and I believe slightly shorter than the s770, when I compared the two, the slimness of the s770 really did make a big difference for me.
The z70 does have some plusses, it seems: lighter weight; slightly more built in memory (though this hardly matters 'cause everybody uses cards); somewhat closer macro focus (although not as low f-stop for low light); somewhat less expensive.
So that's my 2c worth. Hope this helps.
