dakota81 sums it up quite nicely, he chooses to allow his XP2.0+ to run slightly warmer, prefering a near silent PC but at the expense of higher temperatures, he knows, I'm sure, that XP's don't start getting flakey untill they hit the mid 60's C, so as long as your absolute max's stay under the 60C barrier you should be stable with a few degree's to spare.
I joined the other camp of being slightly (but not obsessively) concerned with CPU temps, whilst at the same time I accept there is little to gain by lowering CPU temps on an "unclocked" CPU below that 60C threshold. It could be that the CPU will last for 7years instead of 4, but what does it matter? I'll have my XP5.6gig fitted by then lol.
Of course the lower the temperature the better but not at the cost of an uncomfortable working noise level, a happy medium is probably the best, a system with a couple of low noise case fans and a large copper heatsink with a relatively quiet 80mm fan mounted on it, this would give an average, if not stunningly low CPU temp figure that would fall well under the magic 60C barrier mentioned.
Martin
Replying helps further our knowledge, without comment leaves us wondering.