+1 for both.
I just brought an iPad and i love it. It does pretty much everything an average user would want. And you can get more apps for more or less everything each day.
I brought it as a trial knowing i can return it after 2 weeks but after 1-2 days i was hooked.
Im using it pretty much as my main computer as much as possible - i could use it 100% for everything but you still need a laptop for focused web research/surfing, backing up, loading updates and sync'ing etc etc.
Its nice to type on the iPad in short bursts and maybe its good enough for you but for me the traditional experience of a laptop is difficult to move away from at the moment - this might change. I might be the same speed on both but the experience on the laptop is preferred for longer or more formal writing. And the mbp gives you speed to scan through multiple web pages very quickly - you cant really do that on the ipad browser with its speed. Its fine for browsing but not heavy duty research - just not efficient use of time. Eg, you cant open a link from the page you reading into a new tab to move onto next - its more or less one page at a time going back & forth - all time consuming and messy'ish.
I would recommend anyone get the iPad as it will quickly become the main computer you use.
And the weight difference is wonderful! I was carrying around my 15" mbp pretty much everywhere (3-4 hrs per day on back, with books etc and im pretty strong) but after using carry the ipad for a week there is - stating the obvious - no comparison. Its 4lbs lighter and you know it - its *great* not having to carry that and the extra space in your bag is fantastic. You dont feel it at all and you dont have to be as mindful in making sure you dont bang it on a wall when you swing around a corner (have crumpler messenger bag).
I say get it and move over to it FULLY and see how i goes for 2 weeks. You'll keep it im sure
iPad comes everywhere with me regardless (email, casual surfing, notes/journal, todos, books, pdfs, spreadsheets, podcasts, rss feeds, instapaper app!!!, etc) and my mbp is now pretty much a home 'research' computer and sync station. Probably last longer with getting less wear & tear.