Kindle vs iPad comes down to one simple comparison if you really think about it, what is it going to be used for? I will attempt to explain to you what I mean and help you decide which one is best for you.
The iPad wins this one hands down, with its ease of navigation on websites and navigating all the apps and gizmos that you can get for free or for a small fee just blows the Kindle out of the water. Now the Kindle does have a few things up on the iPad such as the battery lasting a lot longer, I mean a LOT longer. This is not as important to some people as they plan to charge it every night but something to take into consideration at the very least.
As an eBook Reader
The Kindle makes use of what is called e Ink technology which makes it as close to paper as any screen has ever become. This makes it very easy on the eyes and you can read on it for a very long time without getting any sort of headaches. Some people say they don't have a problem with LCD screens causing headaches and can read for a long time with no side-effects, if that is you then maybe an iPad won't be a bad eReader. For those of us who it is a pain, then the Kindle wins with its amazing screen. If you are thinking just because you are on an iPad you won't have access to the large Amazon book store you are mistaken because you can download the Kindle app on the iPad and get all the books just as you would on a Kindle. The best part about this is that if you decide to get both then your purchases are shared to your whole Amazon account!
One more small thing to note is that while the 3G model of the Kindle has free access, as in no monthly fee, the iPad with 3G does require you to pay quite a bit as a monthly fee as it goes through AT&T. There is no other way that I know of to get 3G from any other carrier, maybe there is and I haven't found it but that is something to bear in mind because you won't be able to download books no matter where you are without this 3G function.
As a Multimedia Device
The Kindles main shortcoming is also its biggest benefit, which is the e Ink display. This makes it impossible to view any sort of video. Where as the iPad you can download whole movies to the device and watch them on an airplane or wherever you go. However, they both make very competent music players.
When it comes to games, however, while the Kindle does have some very fun ones (some of which are free) the iPad is pretty much the clear cut winner with real addictive and fun games such as Angry Birds. Games such as this are not even remotely possible on the Kindle.
I am sure you understand a little more about the limitations of each individual system and what they are intended for but to recap. More fun and multimedia, go with an iPad. More book reading and free 3G, go with a Kindle.