You absolutely CAN use it as your primary computer!
As you may see in my signature, i besides do own a Mac Pro which i solely use in the office for "hardcore" video editing. All other computer based work is done on my MBA (a Rev. B 1,86 GHz/128 SSD btw).
I used to have a 20" iMac for my photo editing (Photoshop, Aperture, OpticsPro and other); it also served as a media server to my various ATVs but this now is all done by the Air,.... also i have to be honest,... i am a kind of lazy and did not want to take care of 3 Macs to keep them all synced, neat and clean!
Consider a 24" LED Display and this is all you need,....
Just my 2Cents,....