Re: #8;

Erm, Live View in exactly the same sense as a P&S is not only theoretically possible on a DSLR, it's been done by Olympus, Canon and Nikon with good success.

The only difference is that the DSLR has to flip up the mirrors (which results in the viewfinder and phase-detection AF sensors being blinded) whereas a P&S has no mirror and no AF sensor.

There is no "second sensor" for creating a Live View on any of the DSLRs that do it. In fact, Canon's CMOS party-piece is that individual pixels (or rows and columns) of the CMOS can be sampled independently, allowing the camera to grab, say, every 10th column and row to reduce the amount of processing needed to display a live view. Or the LCD can display a 1-CMOS-pixel-equals-1-LCD-pixel magnified view of a section of the CMOS image. Makes accurate manual focus MUCH easier than using the viewfinder!

Locking the mirror in the 'up' position is no biggie either; Canon for example has had user-selectable Mirror Lockup mode on their entire DSLR range for several years now.

There are other advantages to Live View on a DLSR - Realtime remote-viewing and remote-focusing while in "Remote Shooting" mode; And Silent Shooting on the cameras with electronic first curtains and sometimes electronic second curtains makes little more than a P&S-style "click" as the photo is taken.

I digress.

Re: #8 by SCHMOD:
"Although a "live" view isn't theoretically possible with DSLRs in the same manner as it is on a compact point-and-shoot due to the configuration of the mirrors, a few new models are offering a live-view feature by using a second sensor (notably, the Canon 40D)"

Sorry to correct you, but not only is it theoretically possible to do it in the same manner as a compact P&S, but it has been done several times in the same manner as a P&S.

The body simply flips the mirror up (blinding the viewfinder and phase-shift AF sensors), opens the shutter and begins 'looking' with the main CMOS/CCD sensor, just like a conventional P&S. There is no second sensor, not on the Canon 1D Mk3 and 40D anyway.

DSLRs with Live View either flip the mirror down momentarily to perform AF, or attempt to do an image-contrast focus like a conventional P&S. Neither live-view-capable Canon does the image-contrast focus; they either flip the mirror momentarily (blinding the CMOS chip for a moment) or the user must manual-focus. The Nikon D300 can image-contrast focus. I'm not sure about the Olympus models with Live View.

Manual-focus is probably one case where Live View offers a huge advantage over the viewfinder - on Canons, the CMOS can be locally sampled in a 1:1 fashion, where one CMOS pixel becomes one LCD pixel on the 3" LCD, which makes focussing a big-aperture prime lens incredibly easy; Especially in situations too dark for the autofocus sensors to work (ie: below -1EV).

Just thought I'd clarify that. >.>