Home machine has had this problem almost since I installed 7, although I think upon fresh install it wasn't present.
This has to be reproduceable by Microsoft by now.
In every case that I have investigated this problem has been caused not by drivers or a lack of CPU or graphics horsepower, but by a particular program running. For example, ipoint.exe or sidebar.exe are both known to trigger the problem.
Here's what you should do: Close most of the programs (e-mail, web browser, etc.). Verify that the problem reproes. Now bring up task manager (right click on the task bar at the bottom and select Start Task Manager).
Look at the Processes tab. See if sidebar.exe or ipoint.exe are running. Use End Process to kill them if they are, and then see if alt+tab works correctly.
Now go through the list of programs, especially anything that looks unusual, and End Process them. After each one try Alt+Tab to see if it has been fixed. If you kill a program and that causes Alt+Tab to start working then please share that information.
And yes, Microsoft should absolutely fix this. Complain to them in any way that you can, on forums and support groups. But first check to see if your machine has a new cause, or one of the existing known causes (ipoint.exe and sidebar.exe).