I take off the dustcovers when I'm reading the book (I find them pesky). I put the dustcover back on when once I'm done reading the book. I kind of like the idea of dustcovers -- as long as they're not on when I'm reading! ;-)

I do the same as Dynomutt. Also, the way my memory is getting anymore, the dustcover helps me when I pull a book off the shelf and try to remember the plot, especially in crime fiction series where there are several books. Those little blurbs on the inside covers with the plot summaries have saved my sanity more than a few times.

I try to save the dust covers to protect the book, but cannot read with the dust covers on. I've discovered a handy way to keep track of the books I loan to friends: I remove the dust jacket and put it in a prominent place to jog my memory. (My friends tend to keep my favorites forever.:-)

Being a former librarian, I buy those clear plastic covers libraries use and put them on the dustcovers of many of my books. It keeps them and the books in good shape.

I confess to not only leaving the dust covers on, but using the flap as a bookmark. I tend to be very gentle with my books though, so the dust jacket is rarely damaged.

I am VERY careful with dustcovers - and I protect them from the light. But then, I'm a collector as well as a reader. If you throw away the dustjacket from the cover of a modern first edition, you're throwing away 99% of it's value - quite literally!

I prefer to see books in their dustjackets in a bookcase. A book looks a bit bare without one.

I think contemporary books look better with the covers on. They are also more distinctive with them, hence easier to spot when looking for something specific. I leave them on, sometimes use the flap as a bookmark when I've mislaid the proper one, but am not precious about them (I buy very few hardbacks anyway).

I take them off to read...but put them back on when I am finished. I don't really have an opinion one way or another about how they look, I just feel they are part of the book, so I make sure they go back with the book when I'm finished reading it.

When I read, my books are naked, but they are clothed on the shelf.

I read with the covers on and shelve them the same way.

I often start with the cover on and use it as a bookmark if there is not a real one at hand, but I soon become irritated with the way the jacket rides up and the fear of harming it, so I take it off...but then there is the problem of finding it again when I am through reading!
If I decide to do away with a dust jacket, I cut off its inside folds, if they contain interesting information, and paste them inside the book.

I read my books sans covers, but always put the covers back on them while they are in my shelf. However, I have very few hard covers unless I bought them secondhand....

I've noticed that my local library is slowly phasing out the protective plastic covers that have traditionally enclosed the paper dustcover on hardcover books. I haven't enquired but I'll assume it is a cost saving measure. I've only noticed it in the fiction stacks.