I did go computer free for about 4-5 months with an iPad 1. I loved it to begin with but slowly i began craving a bigger screen, the screen+keyboard on my lap & speed. To be able to switch from app to app fast was a massive miss.
Basically, i always felt constrained using just the iPad.
I have an iPad 3 now and i still use my MBA 13 as much as before. It's horses for courses.
I brought my current iPad 16Gb Wi-Fi specifically as a complimentary device for casual bursts of usage + all my reading. From the previous experience i learnt that this is what works for me.
If you have very simple needs then going iPad only is possible. But for most people i doubt it would work.