I too take my iPad with me everywhere I go. I carry it in my shoulder bag, which I already carried, and it fits inside of it nicely. I carry an iPhone 4 too, so it's basically whenever I'm someplace sitting, I'll use the iPad instead.
I had a pretty steardy portfolio case before, but now with the iPad 2, I only have the smart cover. So I think I'm going to get a skin for the back and a neoprene sleeve to put the whole thing in.
I also didn't want to use battery power from my iPhone if I needed Internet without wifi, so I got the 3G version, that I only activate when I need to.