I've been trying to make an iPad version of my latest app, TrackinU (which was approved just today, it maps your tweets and the route they take). I found there are really not a lot of differences, and in under a week I got a great looking, well adapted app.
TrackinU is typical in that you drill down, touching a person in a list, which gets you to a lower level list of tracks (routes), and further down to a map of tweets.
In the iPad version, I've got a "split view". The right side of the screen always shows a map, and on the left side you have the drill-down list of people and tracks. In portrait mode, the entire screen is the map, and the lists can be brought up in a "popover". Boy, those huge map views are lovely.
Doing this was not much work, I was able to use the same view controller code with bits of conditional compilation added, and I tweaked the interfaces of each view a bit, and changed some stuff at startup for the split view stuff. It was pretty easy. I'll have a universal version of TrackinU ready for the iPad launch.
On another app, Myallo HotList, which also features lists and maps, I tried just recompiling the thing for the iPad after doing a basic Transition in the SDK. This pretty much gives you the same app you have on the iPhone, but the views are actually made larger (as opposed to the 2X graphic chip magnification of the old iPhone app) and this looks decent. Full screen tables, but with sharp text and such. And lovely maps. I wouldn't release it like that though, because a full-screen-width table looks stretched and sparse, but for some apps, especially full screen ones like games, this might get you most of the way there, in just a few minutes.
The nice thing for me is I have one code base, and depending on how I want to market an app, I can use it to make either two apps, one for iPhone and another for iPad, or a single universal app that just does the right thing on the device on which it is used.
All in all, I think we will see a TON of apps adapted for the iPad, very quickly indeed.