...Is there a learning curve associated with "feeling comfortable" when using a stylus to write? In my case, there certainly was; probably about two weeks. But that doesn't mean that I could not use that tablet's functionality from the beginning; it just means that I was a bit awkward at first.
Is there a lag when writing? Sometimes, the first letter or two does not appear on the screen instantaneously, but after that there is no significant lag... at least nothing that bothers me. This lag only occurs occasionally; not often enough to be much of a problem. At all other times, the writing flows very smoothly.
My 2 cents.