Thunderbolt display questions

Purely considering the TB display is much higher resolution than the built-in MBA screen (~3.5 megapixel rez), updating that big screen requires more processing, and thus higher power consumption, meaning more heat.

Also, with so much screen real estate to play around with, it's likely people push their computer harder, maybe without even realizing it. This also generates more heat of course...

I wouldn't let the prospect of the fan spinning stop me from buying a big nice display if that's what I need. Rather, you should ask yourself if the TB Display is what you want, wether you can handle the gloss, for example. It's really really shiny, so if you have any big windows behind your back or anything like that your life will be hell with that display.