I got the case for $25 on amazon...
It's good, but it definitely adds bulk. makes the N900 look even bigger.
The other slightly annoying issue with it is that the extra bulk makes it slightly more difficult to hit the top row of keys. But I got used to this fast.

Other than that glad I bought it. before this I was using a pouch that my wife made for me. I think the pouch caused the N900 to stay too warm at all times (this is bad for the battery) and it made even more bulky to keep in a pocket.

With the otterbox I can pocket it and rest easy thanks to the cover and screen protector.

Hadn't had a screen protector till now on the N900, was always afraid it would affect the sensitivity.
Honestly it hasn't affected it much at all, and now I'm not afraid to use my stylus more on it since I'm not scared of scratching it as I was before.

The screen protector does seem to smudge more though.