I purchased the iPad 2 about a month ago now and I will say that it has been the most useful purchase I have made in a long time! I have not been able to put it down! I am constantly on it - playing games, checking emails, facebook or reading.
I was most excited to download books I've been waiting to read for some time now and that was the first thing I did. Using the iPad I have been able to read about a book a week. It is so easy and fabulous. I can make the font as large as I want and lie in bed with it and don't have to worry about lighting or how close it is to my face. Books download in less than a minute and I love that you can sample a book before you buy it.
I also use it to the newspaper. You can download an app (I downloaded the Sydney Morning Herald) and it updates every day. You can zoom in and read it in large font. I haven't been able to read the paper in years and now I can! You can also get magazines and cook books which is fantastic, as I find most recipe books have tiny font so I can take my iPad into the kitchen and read a recipe with ease.
I think the iPad is very beneficial for the vision impaired, although it is quite expensive and I don't think it can be subsidised as a visual aid. As mentioned previously I purchased mine for free on a plan with monthly data (which works out I pay the iPad off plus a little extra for the data usage) through Vodafone.
The iPad is definitely worth purchasing. It's capabilities are endless.