I have been using my Palm m100 for appointments and reading etexts for two months already and it has been really really nice.
However, after reading a slashdot discussion, I am upgrading, to a almost-new Sony Clie SJ-30
Color vs Black&White (not grayscale)
Higher resolution (320x320 vs 160x160)
Rechargeable battery vs AAA batteries. This means that as long as I remember to plug it every once in a while, I won't lose data.
I can sell the m100 and pay part of the Clie that way, so it's not all that expensive (about US$100 in the end)
More memory (8MB vs 2MB)
Memory stick slot
Almost everyone likes the Clies as far as I can see. Almost everyone hates the m100. Why? ;-)
The only possible con is that with a nice set of Duracells, the m100 could go on for two weeks of reading about 4 hours a day, and the better screen in the Clie will eat battery much faster (I've read about 2-day battery lifes from some users).