There are many reasons for the spinning beach ball, some that Apple can assist with and others that they can't.
Nutshell list of (partial) solutions:
1. Get more RAM (this *won't* remove it altogether)
2. Periodically quit applications known to "leak" (use more memory over time).
3. Make sure you have plenty of free disk space (at very least 4x your RAM).
4. Use Activity Monitor (in Utilities) to spy on the system and applications to find culprits.
5. Learn how to force-quit applications.
6. Give Apple feedback on shifting the virtual memory files into their own partition.
7. Give Apple feedback to clean up memory leaks in Safari.
8. Give Apple feedback to offer a feature to re-open sites in Safari after a quit or crash.
9. Unavailable networks or servers can be a another common cause.
I'm happy to give some potted explanations to the main causes, as I know this list is too terse for non-programmers; let me if that'd be useful.
What Leopard Should Fix: Part One, Kill the Spinning Ball