I was reading though For The Love Of Books (the Blog for Biblio) the other day and they had a great article on cleaning and repairing ex-library books. Which, as they mention, is a great skill to have when you find books that are neat or interesting but don't necessarily have a great monetary value. The day I find an ex-library Hemingway first I’m taking it straight to a specialist but in the mean time I shall pay heed to these valuable tips:
If you're determined to remove a library pocket, you can try such products as un-du Label and Tape Remover, followed by a minute or two of low heat from a hairdryer. The multipurpose Document Cleaning Pad can help in removing residue.
Rehabilitate enough library books, and you'll become intimately acquainted with rubber cement. To cope with its removal, try a long-lasting crepe rubber eraser called Pik-Up, which works on many other adhesives, too.
Then they go on to describe some products and tricks for restoring dust jackets...
If any of our readers have done any book restorations themselves and have before and after photos I would be most interested in seeing what an armature restoration job can accomplish.
(edit) - The book Helen suggested, in her comment below, is Book Repair for Booksellers by J. Godsey, in case any of you were looking for it.