That depends. Personally, on my MBP, I use Photoshop, Sketch Up, Word, and a bunch of other programs daily that I just wouldn't be able to use on the iPad. But if you're the type of person who just uses their laptop for web browsing, e-mail, and iTunes, it could definitely replace it.
No for me. My MBP is my productivity machine. The iPad is just an entertainment device for me when I'm lounging about, not really doing anything. That was the system I had with my iPad 2 and it worked fine. I plan on following the same setup with this new iPad.
I was just asking, since I am finding that I am not traveling with the MacBook as much, and the majority that I do, is Safari, email, and some iTunes. So it seems like it may be worth it for people like myself, who does "real" work on my desktop the majority of the time.
When I bought the MacBook the iPad was not an option.
I'm basically replacing my MBP with iPad for mobile needs. Since the only things I really need on the road are email, web, and a few apps, the iPad works nicely and reduces alot of weight from taking my 15 inch MBP everywhere. For anything requiring more processing power at home, I've got a mini and that arrangement seems to work well for me. I think how practical it is for you really depends on what your needs are when you're away from home.