I have always been a fan of the 7 inch tablet. It is ultra portable, but large enough to use it as a tablet and not an oversized phone. I have not replaced my laptop, as there are a lot of things that a tablet is limited on (hooking external HD up, smaller internal HD, connecting and programming other devices etc) but I would think that if I was looking for a tablet to replace my laptop, I might go 10 inch or larger. I am thinking about getting the MS Surface tablet when that comes out to replace my laptop.
I use the 7 inch tablet to access the internet, watch movies, play music etc when I am on the road and a laptop is too cumbersome to bring with me.
The development potential is what spurred me to buy the Nexus 7. I bought the Kindle fire when I saw how much development was being done on that (and it was $139 at the time), but I think the Nexus 7 will be a more robust development community.