I went for an i5, my corporate machine has an earlier i7 which does a fair impression of a "hair dryer"

I know it`not "Apple for Apples"

My i5 idles at around 40C and so far has not ramped up the fans. Playback of an iTunes movie will see CPU temp rising to low 50C`s, ambient is around 25C.
Still loading software, so we will see so far very impressed with the new air, runs cool and compared to my "toasty" MacBook Pro 2Ghz 4.1 blazingly fast.
I am running SNC Fan Control as it is just an application, it installs no startup scripts, background processes or daemons. You can choose to start manually or on login, at the end of the day the more system monitors, processes etc the bigger the impact on the battery life. With SNC I can see CPU temp and fan speed which is good enough for me, ans can set default`s for Battery, AC & Charging, which is very useful as it far easier to keep a system cool, than try to cool a hot one down...
The i7 has a place for some, yet for the vast majority the i5 is more than enough. Short of the odd video encode I would never stress the machine.