The installation experience and stability depends on the hardware. Of course, that's a usual experience with a Beta version.
The best experience is with my newest tablet PC: Fujitsu Siemens Lifebook T5010.
Installation (upgrade from Windows Vista) was smooth, every device is available, so far no major issues. I could also run Microsoft OneCare after telling the application it's running on Windows Vista.
With a slightly older model (Lifebook T4220) installation (upgrade as well) was hanging near the end of the installation during a check of the graphics card. After turning off and on again the installation completed without problems. Checking the Windows Experience Index on this system either results in a hang or a blue screen. However, for normal daily operations this system doesn't have issues.
On a old notebook (HP Compaq NX7000) a new installation of Windows 7 was running fine. For the graphics card just a standard driver was installed during installation. With an update the driver for ATI Mobility Radeon 9000 was installed, and as a result the screen on the display flickered. The display on an external monitor is ok. Rollback the driver. The standard driver just has a Windows Experience Index of 1, but the system is fine for non-display related tasks. I checked the HP Website for drivers, but only Windows XP drivers are offered for this notebook. I used this system for Windows Server 2003 which was fine. It's great that Windows 7 is running on this system as well!
Here is a link for the experience with other systems: Sammelpost: Erfahrungsberichte zu Windows 7 Beta