Is there anything wrong with reading Birkhat HaMazon from a computer? E.g: http://www.jewishvirtuallibrary.org/jsource/Judaism/birkat_hamazon.pdf
I often use that link to make birkat hamazon after having a meal by the PC and find it more convenient than using a siddur.
Am I yotzei?
I guess this question could be extended to other tefilot that could be said sitting such as tefilat haderekh.
There is nothing wrong with reading from a computer, provided of course that one is not distracted by other content that might be available.
In the times of Chazal, none of the prayers were printed, and they were recited by heart (in fact, it was forbidden to print a siddur, for fear that the Names of Hashem would be erased by a fire on Shabbos). Today, prayers are printed, and this helps us to concentrate, but there is no difference between reading them from a printed book or from a computer.