OP here. The text is comfortable to read. i.e. I made it big enough to be comfortable. I haven't experienced any of the eyestrain that others have mentioned, despite spending up to 2 consecutive hours playing with this app.

However, in addition to the low resolution in the current Oculus dev kits, text rendering is definitely hard to do in VR. How do you do crisp sub-pixel rendering when your face is ever so slightly tilted? Something that will have to be solved in future software or by sheer pixel density.

That said, it's early days for VR and the future is bright!