Our F350 has a matching truck cap and we love it..especially for camping. It's SO nice to be able to haul stuff back there without worrying about it somehow flying out, being stolen if we stop somewhere, or getting exposed to the weather while we travel. Not only that, but it's handy at the campgrounds to throw stuff into the back if rain suddenly comes and we don't want to put everything under the awning.
I mean, there are the negatives of making the truck a bit more cumbersome to handle (line of sight, etc), and certain things depending on height will not fit back there.
However, to US the positives WAY outnumber the negatives.
As far as taking it off, well, our truck has the 8 ft. bed, and that cap weighs a TON. I only took it off twice in the time we've owned the truck, and I won't do it again.:B