Cleaning Old Paperbacks

Flick the pages a few times (you might want to wear a mask or mouth-protector of some sort) then take a damp - in fact, nearly dry - cloth and wipe down the page-ends when the book's closed. Also the spine. But it has to be a damp cloth to pick up dust bunnies (and nearly dry to prevent damage to the books).

Damp dust the shelves they're going on then buff with a paper towel.

Baking soda

http://www.signonsandiego.com/uniontrib/20080922/news_1c22heloise.html

I got a bunch of old musty paperbacks at a garage sale once, and some of them were pretty gross. I used some of those little alcohol wipey pads that you can get at the pharmacy. Cleaned them up nicely, left no damage, and eliminated most of the smells.

Others have suggested cleaning the covers which you should do (see video below), but I doubt that would get rid of the musty smell when you open one to read.

You can have a fan blow on them (try to 'fan' the pages open at least slightly, so there's at least a little bit of air circulation between the pages) for a few hours or days, or perhaps longer, depending. Do this in a place that's ventilated, or at least where the 'bad air' won't bother anyone. I've done that and it can help immensely.

There's also this, though I've never used it:

http://www.sicpress.com/bookdeodorizer.html

I understand using both that and a fan, as in inside something like a closed, turned-off refrigerator, is the fastest.

There's also this how-to book with lots of cute info, I have an "earlier edition," pre-2006 of it:
http://www.sicpress.com/bookrepairforbooksellers.html

There's supposed to be a video for "cleaning surface dirt" here:
http://www.sicpress.com/videos.html#cleansurface
but I found it here:
http://www.youtube.com/watch?v=4815oKGbsPI
Joyce (at sicpress.com) has lots of other book-doctoring videos.