Well, that is possible now. One option are the smartphones, specially the incoming new generation with screens of up to 4 inches or even greater. In today phones it is also possible, but possible the screens are too small to do a decent reading and they are useful more like a way to consult a reference in a given moment that to do regular lectures. There are some workarounds that work for plain text, but are not too good for physics/math pdfs. Also you will need to be sure to know what software to get. For example for android operative systems the only decent way seems to be to go to the document to go suit. For windows mobile, Symbian, or even the Ipne OS there are wider variety of options.
But even with the incoming generation of mobiles (which are lovely anyway because of the many, many features they have)it is better to search for more comfortable options.
In this sense there are to main ways, the internet tablets and the tablet PCs. In fact the different among them is not too clear (possible the internet tablets are smaller). This year, possible inspired by the rumour of an "apple tablet" there are many, many new tablet PCs in the way, covering different ranges of prices and features.
I have decided not to wait and I have purchased one of the first available ones, an archos 9
The name makes reference to the 9 inches of the screen size. The OS is windows 7. There in the market products with 7 inches screens, but I think that for a comfortable reading 9 inches is the minimum size. Also influenced me that the archos 7 (or archos 5 for what matters) used android, which is a baby OS.
So now I have in a device of a size and weight of an slim pocket book all the reference material I could wise (in pdf or djvu format), and I even can run mathematica (I prefer it over matlab). And of course I can do all the other things that one can do with a normal computer. Ok, the performance is worst that in a desktop computer) and a touch screen is not as good (for my taste) as a regular mouse and keyboard. But still it is lovely the possibility of doing physics everywhere. And, anyway, it is not a good idea to charge that computers with too many programs if one wants a minimally decent perfomance.
Well, for sure that has been already possible since a few year with regular notebooks and ultra small notebooks/netbooks, but I think that the tablet PCs make an actual difference. It is definitively fine to keep reading the same arxiv pdf you were reading in your home while you are in the bus or the underground (without the need to fill your house with too many printed papers).
By the way, an important tip. Most pdfs have wide margins that make their reading in a not too big screen awkward (the zoom options of the reading programs not always solve that problem in a the satisfactory way one would expect). It is a very good idea to get a program to crop the pdfs such as Nitro pdf or pdffills. Of course these programs have many other possibilities that just cropping pdfs, but possible that will be the one you will use the most (the second one could, maybe, create pdfs scanning your favourite books).
Well, the technology gives us great possibilities. Lets hope this decade would be better for physics that the past one that, I coincide with Jester (resonances), is possibly the worst in hundreds of years.
