The key design and character screening are good overall. The letters are screened on and are a subtle cream colour, not stark white. I think it's attractive looking. The only downside in my book is the windows key, but nothing to be done about that.
It's a great size. Without the keypad, it doesn't look like a giant black monster sitting on the desk and it means the mouse is always nearby.
Remapping the keys to work with OS X was no problem at all. The Windows key becomes the Option key and the ALT key is the Command key.
Since it's a keyboard, clearly the way it feels when typing is the most important consideration. After a day of moderate to heavy use, I'm very pleased with how it feels. The keys are springy, with quick action. It doesn't take much force at all for a keypress to register, so your fingers can move from key to key quickly.
I've used both the stock Apple keyboard and the Microsoft Natural Keyboard 4000 quite a bit. Switching back to the Microsoft keyboard briefly, its keys felt squishy and unresponsive after the Filco. I still like the feel of the Apple keyboard, but I find I'm faster and more accurate with the Filco.
I have had some minor RSI problems in my wrist. Lately it hasn't been bad (typing on the Apple keyboard). So far (today), I don't notice any change after using the FIlco. I think it will take longer to be able to state whether or not this keyboard is better or worse for that.
As with any 'clicky' keyboard (I went with the Cherry Brown switches), the keyboard makes quite a bit more noise than other types. After using it for most of the day, my co-workers didn't comment on the sound until I asked them about it. They said it didn't bother them and that they hadn't noticed until after I mentioned it. I haven't used a keyboard with any other colour of MX switch (red or blue), so I can't compare.
I really like the noise it makes when typing. It may be kind of silly, but it really reminds me that I'm getting something done. I feel like I have a lot more momentum when typing and I pause less, thus reducing the number of times I might distract myself. This may be because it's new, but we'll see how it goes.
After one day of use, I'm really happy with it. The only thing I'd change is to add a couple of USB ports, but that's not a deal breaker for me.
Update: I can report that the keyboard works with the iPad using the USB camera connection kit. It was a bit finicky at first, but it works fine.