I stand corrected…
After spending the better part of a week with the newest version (4.3) of Google Earth on two different models of laptop (one with only 512M of RAM, both with on-board graphics cards) and five different desktop computers (ranging from 512M - 4G of RAM and four different graphics cards) on three separate networks, I really must say that I stand corrected concerning GE’s performance and impact on lower end computers.
The more I use it, the more impressed I am by the performance improvements, especially the right-click zoom and rotate feature. If you haven’t tried it yet, simply right-click and drag anywhere on Earth.
The effect is smooth, quick, easy to control and is a whole lot faster than using the slider control and there is no need to go into the options window to change your fly-to speed.
Another significant improvement is the relatively blazing speed in switching between Earth and Sky. I honestly used to hesitate to switch due to the lag time that would allow students to get slightly unfocused. Now, however, the switch is rapid and clean.
As to StreetView and 3D Buildings, there is a negative performance impact, but it is less than I thought. Due to the GE Team reprogramming how 3D buildings are delivered and rendered, it is a lot quicker to load the models now than before which can allow you and your students to focus on topics of interest, rather than twiddling your thumbs while the models loaded. It does seem to be the StreetView imagery and placemarks that slowed down the computers I tested it on, partly due to the rendering of the ’snapshot’ arcs and spheres.
I can see how lessons, like those created by Noel Jenkins at Juicy Geography where land use/urban planning and analysis plays such a key role, could really be enhanced by literally immersing the students in the urban environments under study.
The current version is still, officially, a Beta version meaning that improvements and bug fixes are on the way, but in the meantime here are a couple tricks I found work to alleviate two odd issues I discovered:
1. Rather than displaying the longitude and latitude, etc. at the bottom of the screen there appear to be random numbers flashing around. To resolve this issue open Tools:Options and under the 3D tab, switch from OpenGL to DirectX rendering (or the reverse).
On the Gateway Profile computer with a PCI Nvidia graphics card in the lab that was exhibiting this behavior, it fixed it right up. You might notice a strange blocky rendering pattern on Earth’s surface after you switch, but as the imagery comes in clearer the blockiness disappears.
2. The Sunlight, Day/Night function does not show the correct shadow for the time of day it is (accompanied by odd letters and digits on the time slider). Click the clock symbol by the time slider 
to open the time options and put a check in the box that says ‘Restrict time to Selected Folder’
, click on the Primary Database icon in the Layers panel and it should clear up the problem for a while. I almost think that the issue I saw was more due to a conflicting time animation somewhere in the Places (buried in the tons of placemarks or Layers on that particular workstation) or Layers than an actual problem with the Day/Night option.
Speaking of the Day/Night, the Google Earth team added a subtle, yet beautiful, feature for computers with high-end graphics cards. Shadows, lighting and even starry skies! Tilt in a mountainous region at dusk especially and the effect is bound to be inspiring to your students!
Another little bonus is the fact that the Flight Simulator mode is now a menu option under the Tools menu.
Not only is flight entertaining, but with the speed and altitude indicators there must be some fun math activities that could be created for students. I will leave that up to talented teachers like Thomas Petra from RealWorldMath.org or you 
Frank Taylor at GoogleEarth Blog has a number of excellent tips on how to make Flight Sim mode more effective and enjoyable for you and your students, while the Google Earth manual lists over two dozen keyboard commands you can take advantage of while you fly.
Oh, one last thing while I have you here. Does anyone know why in the world there is a very large, very perfect equilateral triangle in the middle of the desert (kml file) near Phoenix?
