I also bought the new 13" 2011 Air (with the 1,7Ghz i5) and it also is not hotter than expected but way more noisy!
Some people are reporting no issues but with browsing non flash content I often hit the 55-60°C marks wit the fan around 2000rpm, the real killer is any kind of HD web video (flash but also html5), it slowly cranks up the fan to at least 5500 rpm stabilizing the CPU temp at around 70°C.
That is almost the exact same behavoir I get from my old MacBook (white unibody 1 1/2 years old, SL), which also peaks at 70°C and 5500+ rpm.
I'm just unsure what/if something is wrong due to the several different posts of people reporting no high rpm issues with several concurrent flash videos running, while others are reporting general temperature and rpm increase with lion.
Good thing i have an AppleCare Protection Plan and an authirized service provider around the corner where I might take this Air soon if there are no signs of this issue being mitigated by software fixes.