Neil Balthaser at Ultra Mobility (http://ultramobility.blogspot.com/2007/06/oqo-model-02-review-form-factor.html) reviews the OQO, one of the smallest tablets (5 inch screen) on the market. He has some very positive things to say about this tablet especially the handwriting functionality. I suspect that this is due to the fact that the OQO sports an active digitizer.
While I have not had any personal experience with the OQO, I did get to try out the DualCor tablet (not currently shipping), which had a very similar form factor. While a 5 inch screen might seem a little small, the text was still readable and I was able to fill out an Active Ink form quite easily after I configured the program to allow for the size of the fields to expand as I write.