I have curnently got a 11.6" macbook air, before that had a Al unibody macbook for school. I really like the air size & weight -even though the pricessor is slower -because of the flash disk storage i have not noticed a performance downgrade -PS ele8 is the hungriest program i use. eithe ris great -the 11.6" is a little small - 13" is a great size, my work colleague bought a 15" mb Pro - he now recognises its a little big -
Me i would stay the air (though get the $99 superdrive)
get your son to try bot-its a personal decision
a leopard desktop shoudl be blank -i hide the dock & keep all crap off so i have a lovely clean workspace (its the MAC way)
PS i always buy from the apple store - 3 reasons
1. they have a used/demo section at the bottom of left on their shop site- some great bargains
2. they usually give free shipping which is quick (most my stuff arives in 2 days)
3. click on the education store tab at midlle left of the store screen -say you are a K-12 teacher & save $60-100 on your laptop

- they do not check & you get a great price

{though i really am a teacher -there definition of education is really loose, if you teach someone on the street astronomy/or you go to a 1/2 day camera course you qualify as a student)