Great when showing property. realtor.com and foreclosureradar.com offer some really great apps. They support both platforms. I use ipad and it's been very impressive when I';ve been out with clients as they app is using the built-in gps. This means realtor.com shows homes that are for sale or for rent where you are. You can zoom in/out and look at photos etc. Same thing with foreclosureradar. It shows homes that are pre-foreclosures, scheduled trust deed sale etc.
I would recommend to have the modem built-in so it's less hassle when you're out w clients.
In my opinion, the ipad does not replace the computer. I recently switched from PC to Mac and it's super fast.