I upgraded SuSe 7.3 to SuSe 9.0 a half year ago, and ever since my system is very instable: I get frequent (but rather random) system freezes (sometimes two or more times a day), and file system corruptions, too.

Even the first time when I wanted to start the upgraded system kde did not start, because there were file system corruptions on the /home partition.

However, I feel as if the freezes were more frequent when I am connected to the internet, and, especially when I use Mozilla (and ssl) to connect to my office network.
But it it happens when I use opera, too, and it also happened once when I had no internet connection.

I realized that I never have system freezes when the system is idle, or when I am watching movies with mplayer.

I never get any error messages anywhere when the system freezes, so I have no idea what is causing the problem; however, I have been using SuSe from its version 6.4 and I have never had such serious problems with it.

Could you give me a hint what to check?

By chance are you using a winmodem driver or any other odd hardware that has a driver you installed yourself? Try using YaST to add acpi=off and noacpi to your grub/lilo command line. Run memtest86 . Post back