Much to my chagrin the problem continued well after I had stopped using good ole Minefield. I began to explore running processes via activity explorer and just generally clean up my machine. So after uninstalling a bunch of apps and services I wasn't running anymore and still experiencing the same problem.
At this point I was worried because the cpu was not the issue, iTunes would continue to play with no problem (and even respond to the hotkeys on my keyboard for switching tracks) it was just the UI that was freezing, and generally as I was opening files. Disk issue? Memory? Maybe even something where the network was introducing some latency? After some googling and consternation over my potentially failing disk I finally did what I should have in the first place and started to dig into the system logs via Console.
Sure enough one group of messages stood out right away...
06/09/08 9:21:29 PM com.apple.ATSServer[14462] ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
06/09/08 9:21:29 PM com.apple.ATSServer[14462] 2008.09.06 21:21:29.63
06/09/08 9:21:29 PM com.apple.ATSServer[14462] ATSServer got a fatal error (status: -4) while processing a message (id: 20) from pid=14309.
06/09/08 9:21:29 PM com.apple.launchd[386] (com.apple.ATSServer) Throttling respawn: Will start in 10 seconds
06/09/08 9:21:39 PM com.apple.ATSServer[14465] ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
06/09/08 9:21:39 PM com.apple.ATSServer[14465] 2008.09.06 21:21:39.90
06/09/08 9:21:39 PM com.apple.ATSServer[14465] ATSServer got a fatal error (status: -4) while processing a message (id: 20) from pid=14309.
06/09/08 9:21:39 PM com.apple.launchd[386] (com.apple.ATSServer) Throttling respawn: Will start in 10 seconds
06/09/08 9:21:41 PM quicklookd[14463] [QL ERROR] 'Creating thumbnail' timed out for '<QLThumbnailRequest /Library/Fonts/LiberationSans-Regular.ttf>'
06/09/08 9:21:50 PM Console[14309] Failure with ATSFontGetUnicodeCharacterCoverage(). Disabling font fallback optimization for characters not renderable.
06/09/08 9:21:51 PM com.apple.ATSServer[14468] ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
So the ATSServer (Apple Type Server) was choking and it looks like the beachballs I was seeing were related to the throttling of the respawn of the server. So I'd be staring at a beachball for up to 10 seconds while the rest of the OS hummed along fine. A quick google search revealed the most common reason for this kind of failure is a corrupt font. At this point I shot around in my chair and asked my wife pleadingly and only somewhat accusatorily whether she had by any remote chance installed any fonts lately..... Yes. So I gave her control of my screen so she could clean up what had been added and like magic the beachballs ended. No reboot or anything required, ATSServer has not crashed since and I am writing this in Minefield 3.1b1pre with no problems! (sorry to blame you firefox)
Sadly I do not have the patience to go through the exercise of finding which fonts specifically caused the problems. I really don't have much use for the extra fonts so I'm just as happy to have them all gone. Still hopefully this helps someone.
Now if I could just clean up all these damn mds errors that keep cropping up ...
mds[34]: (Error) Import: importer:0x84b600 Importer start failed for 501 (kr:268435459 (ipc/send) invalid destination port)