Once per minute, Windows 7 writes a timestamp to disk. This enables diagnostic tools to check whether and when Windows has been shut down unexpectedly. For home usage, you can safely disable the timestamp. This reduces write access to your hard disk.
The new Windows is pretty stable. Once installed, it usually works like a charm. However, even the most stable operating system can run into problems, for example if important system files get corrupted due to hard disk failures. The good thing: Windows 7 ships with a repair feature.