While the iPad is generally meant to be a link in products from the iPhone to the MacBook Pro it has a vast number of functions that can be compared to that of the MacBook Pro. The iPad is considered a tablet PC and offers the ease of touch screen technology and portability. The MacBook Pro is considered a laptop PC and offers a bit power and functionality then the iPad while still being reliably portable.
Users of the iPhone may find that the iPad offers much of the same features as the iPad. The difference between the two being that the iPad has a much larger view area. If you are looking for a gadget that offers some basic functions of a PC such as internet, e-mail, word processing, and some applications then the iPad is perfect for you. The MacBook pro on the other hand is a fully functional PC with many more capabilities and infinitely more digital storage space. When designing the iPad I think Apple leaned a bit too much towards the iPhone.
While the size of the iPad is much more convenient to carry around then the MacBook Pro, users will notice a loss in power due to it's smaller size. Being one of it's major selling points, the size of the iPad has been reported to have over heating issues when exposed to direct sunlight. Most major electronics are not meant to handle the heat of direct sunlight over extended periods of time however with something like the portability of the iPad, designers should have taken this into consideration.
The MacBook Pro has been on the market for much longer then the iPad. I am sure that the MacBook Pro had it's share of quirks when it was first produced as well. If you are thinking of adding an iPad to your gadget arsenal consider waiting till the second model comes out. This will give designers a good idea of what can be improved on and you will not be spending your money on a prototype model.
All in all I think at this point the macbook pro has my money. I personally own an iPhone and a laptop PC. I can not think any reason why I would want anything in between. If the iPad operated more on level with the MacBook Pro I could definitely see the attraction to this gadget's portability perk. Before completely putting the iPad out of mind I would like to see where Apple decides to go with it in the next few years.