The Kindle isn't really designed to take individual notes, even though I desperately want it too!
The notetaking function really is just for minor scribbles to 'book' margins.
It is first and foremost a reader.
I was surprised how well the keyboard responded despite reading reviews to the contrary. The chiclet-like keys have a little snap and don't feel mushy.
Also the mostest, bestest, underrated function is Search

all your notes are indexed and can be searched off the dedicated 'search' key. I think it is super awesome, as my wife's Sony Reader lacks that.

if you type too fast, input is stored in a buffer and will output over time.

The unfortunate aspect is that you can only add notes (6 lines per screenful) to individual lines in your document (stuff in your library). You cannot edit a whole plain text file. (I've since sent that as feedback, knowing it is not feasible) heck, I want a shell like my Asus eee or the iliad folks!

The note field will extend beyond 6 lines and show another set of 6 lines, but I have yet to find any arrow keys to navigate vertically in the note. alt + h and j will move the cursor horizontally so that is something.

Additionally like the iphone, there is no copy/paste.

Also every edit to a note will be recorded, date stamped and captured in your MyClippings file with duplicated lines. So if I make a note: "Read The Joy of Living" and save it, then go back and edit the note again to add "Buy Genuine Happiness", My Clippings file will show redundant entries for "Read The Joy of Living"
I'm still trying to work in some lite GTD as I find the kindle my most carried device. But since there is no monospace fonts nor can users add fonts, my calendar still turns out malformed: for month in `seq 1 12`; do cal $month 2008; done

But reality is that the slowness of my data entry, makes the Kindle impractical for any decent rapid notetaking. It serves more like a journaler for writing when I have a cache of time- on bus, medical appt, etc
Twitter works

but still the time it takes to log it is a chore.
In a way I think that is good that the UI constrains the wireless, so we can still have it 'free'!
I think the ultimate would be that epson controller chip to allow scribbling like the Iliad for Kindle 2.0. This coupled with free wireless would be paradise.