100Hz would be good to have if you are not paying any premium for it. When I was in the market looking for a 40" LCD, I had considered SAMSUNG 40B530 & 40B550 along with SONY 40V550 & 40W550 (100 Hz). But at that time SONY was asking just too much premium on the SONY 40W550 (90K). Finally I settled for the SAMSUNG 40B530 which does not have any 100Hz Motion Plus. It has been a few months now and the ticker symbols at the bottom or a Cricket / Football game (fast action), appears just perfect. Even Wildlife programs on National Geographic & Discovery Channel appear very nice without the 100Hz. Have connected a XBox 360 also to it and gaming is just fine too.
So, in conclusion, if 100 Hz Motion Plus / Motionflow technology comes with a reasonable price tag, go for it. Otheriwse a good LCD [i.e. excellent picture quality, good contrast, good viewing angle etc.] without 100 Hz should be fine too. Best is for you to take a demo and make the final call.