This is my experience after using my Kinesis Advantage for six weeks:
Non-staggered layout: It was very easy to get used to enough to use it full speed, but somehow I still don't feel completely at home on it. I still sometimes hit 'b' instead of 'v'. Maybe it's because I still use the staggered keyboard of my netbook regularly. The number key locations are brilliant -- for the first time, I can touch type numbers!
Cherry key switches: Nice! I'd sure like to try some reds, but the browns are nice as well.
New locations for some keys since I use the rightmost keys for Scandinavian letters: The apostrophe, tilde/caret, accent/pipe and some other keys have moved. It's not as much of a problem as I'd have thought. Acceptable.
Arrow keys: A pain to use them with one hand (just like the rest of the keyboard) but it's awesome not to have to move the hands when I use both. When I use other keyboards now, I get disappointed each time I reach for the arrow keys but realize they're not "there" :-)
Thumb keys: Really good. But the thumb modifier locations are still not second nature.
Pedal: I use it as the standard keypad shift. It's nice to have but not as good as I'd hoped. I use it if my foot is nearby, not if it's not.
While the keyboard is very comfortable, I'm not sure I'm going to buy another one soon. I miss the editing capabilities I have perfected for years on the arrow and nearby keys.