I agree with James that it is better for everyone to have a monitor that displays images for the clients at a separate location than the tech, and I also agree it is very important to be able to see the focus as you are shooting.
As a digi-tech I run across the situation where focus slips off the eyes and a quick word to the photog saves a bunch of images, so that is a must.
But i've been running 4.5 since it came out and can't see why we can't satisfy both of these concern.
If when shooting, I "show viewer" (under window) it opens a separate window that can be used only to view the selected images and has its own control for zooming. So the client can be starring at the whole image on one monitor and I can be clicking around checking focus and messing with tools on the other one and everyone is happy.
Similarly, you can set up the client monitor with a compare image of their choice and have it sit on the screen as new images pop up next to it. Seems good to me.
I haven't run 4.5, (though we are loading it on a pc to see how it tetheres to a Canon). I probably won't use 4.5 until December at the earliest due to schedule and I don't like to introduce new anything when there is a lot of pressure on the schedule.
So I will have to say I don't know it's functions and it may do everything I eventually need.
I do know very well how clients review a session and edit and their requirements and it's much nicer for a client if the captured image is large, the session is on a seperate monitor so they can go back and call up some images for review before we move on.
It is also much nicer for the digital tech if the clients are close but at another station. We routinely run a second 23" or 30" monitor to the clients so the tech can do his/her work and not be distracted.
As far as focus, whatever, but I guess it depends on how you shoot, how much is going on in the room and it also depends on the shot. Focus can be easy or hard, but in the world of digital focus is very critical and seems to be less forgiving than the film days.
I just shot with the 110 F2 on my contax's and everything close up was dead on, everything further back we had to adjust for some back focus, but then again I shoot a lot very close to wide open so there is very little room for error. Having the 3.78 window was nice and made it easier to adjust quickly on a busy day, without interfering with the clients view of the shoot.
On these instances it's great when the tech catches it early, we adjust and then everything is fine.