My now 4 yr old MBP has been a great machine - My first Mac and my first notebook. It's been great at releasing me from sitting at a desk hour after hour. I haven't sat at the office desk for general computer usage in 3 years now. I sit in my recliner in front of the big screen and get to sit in the same room as the wife instead of us being at opposite ends of the house half the time in front of my dual and triple monitors. One to browse, one to watch TV and one to be playing the latest game.
Of course, at that time as a hardcore gamer, I had spent years walking by the Mac aisle in the stores as useless pieces of junk to me as a gamer and overclocker. So, I wasn't ready to just kick my Win machine out of my life.
Knowing what I know now and the advance in what's available, my choice would be different today. Today I would go with the iMac and an iPad instead of the MBP.
The MBP is a great machine, but it is a heater sitting on your lap. Yep, it gets warm to say the least. So now you get a laptop stand. That works ok. But, where do you set it when you need to get up for a minute - the floor, the arm of the chair, need room on the side table to set it down - run electrical cords to your favorite spot to keep it charged - another to connect your external backup drive - another to connect your iPhone, iPod, etc...
You'll definitely need a laptop stand when you carry it to bed with you just to keep the rear vents clear so it can breath. You'll find yourself wanting to carry it all over the house and use it in places you've never been able to before.
With an iMac you'll have all the same functionality you've always had, along with a bigger hard drive, better video card, 27" screen... With an iPad, I don't know where to start. It can go everywhere - the LR, BR, bathroom ;D... No heat - what a joy. Want to lie down in bed instead of sitting up cradling a notebook in your lap and browse the web a little, read a book, your favorite magazine, listen to an audiobook, catch a TV show or watch a movie before you go to sleep. For all of those things the iPad just flat blows a notebook out of the water related to it's convenience.