Open apps: Firefox 3, Safari, Camino, Adium, Smultron, Twitteriffic, Marsedit, Activity Monitor (this always open), Evernote, Shovebox, Skitch, GetDropbox. There may be others, there may be less. It is NOT Spotlight – that is fully off.
Symptom: If I click a dock icon it opens Finder. If I click a link it opens in a new window. The HD grinds. The processor goes to 100% and I end up pressing the power button.
Happens: Daily just about.
Annoyance factor: off the freaking scale. Don’t these thing “Just work”?

So, given the above apps are established (and this happened in FF2) what is the problem? What did I do to break things? It can’t be the machine right?

The only possible thing I do differently to possibly someone else is that I open and close dozens and dozens of tabs in a relatively short space of time. It’s not for fun, it’s work and i’ll be damned if I need to change my work pattern simply because a computer cannot keep up. I lose a stack of work every damn time this happens.
All I can actually do is rearrange open apps so I can constantly see the Ctrl-Alt-Del equivalent the Activity Monitor and see what locks up.

If this was a PC some Mac owners would be having a go at Microsoft……