Wow, at least I'm not alone here.
I've had what both AlanH and Txurce describe happen -- and actually to a much greater degree of slowdown than described above (although this may be b/c, as Alan has wisely not done, I stubbornly keep playing instead of wuitting and restarting; if it is a "deterioration"-type problem.)
Anyway, I have notice Txurce's problem -- after moving all the units the "continue" button flashes slower than usualy, and scrolling the map is slow and choppy.
Additionally (not sure if separate problem or related) it will sometimes slow WAAAAAY down -- my tip-off if usually that the music will stop playing, which causes me to notice that units aren't animating, etc. After some time (15-20 seconds) it might play a short section of music, advance a frame of unit animation, or I'll hear a bird shirp or a wolf howl or something. Then still and silent, then repeat. I can still click on dialogue boxes, or pause, or quit, but it's all massively delayed (again, 15-20 seconds minimum.) Throughout this, however, my mouse pointer moves normally on screen.
Usually right before this happens I can hear something "spinning down" in my Mac -- HD? CD? Not sure. At least once when I was really patient it seemed to come out of this slowdown all on it's own, which was indeed accompanied by the sound of whatever spinning back up.
Also, I have only noticed this when playing the GOTMs, and I first had it happen on GOTM-17 (carthage, that was 17 right?) which was pre-1.29 beta (btw Brad, THANK YOU THANK YOU THANK YOU!) Didn't play Celts (out of town all April).
Any ideas?
10.2.5 on a 500 Mhz G4 Cube 1.25 Mb RAM plenty of HD space.
-sirromdivad