I have a misbound copy of a book, what is it worth? - Misbound copies do happen and can take many forms. Upsidedown binding, missing pages, repeated pages & pages out of order are the most common types of misbindings. Although some people do collect these misbound copies, in general they do not add to the value of the book. At best an upside down binding could add 5-10% if you found the right collector. Issues where pages are just missing though, make the book less readable and would lower the value up to 5-10%
I have a regular copy of "insert title here" signed by SK, how much is it worth? - A genuine Stephen King signature usualy adds between $200-$250 to the value of any book. So add that ammount to the value of your regular book.
I have a copy of "insert title here" and it's missing the dustjacket, how much is it worth? - Up to 90% of a book's value is in the Dustjacket, especially with early Stephen King works. The reason for this is that the early Doubleday books were made very poorly and the dust jackets were especially prone to ripping, so finding copies with good dust jackets is difficult. If your copy is missing a dustjacket it's almost never worth very mutch, if it's also not a first edition (and you can check whether it it or not by going to the appropriate section on the site), then it's only worth a couple dollars.
I have a copy of "Insert title here" and there's no price on the dustjacket, is this a 1st edition? - Any book without a price on the dustjacket is a book club (BC) edition. BC editions are not the same a 1st trade editions and are generally not collectable. Their value is only a few dollars. Often these BC editions will look very similar to an actual 1st edition except for the missing price on the DJ. This is why the DJ is such an important piece of the books value.
I have a limited edition book with "PC" instead of a number, how much is it worth? - Books labled PC (Publisher's Copy) are generaly very similar in price to their numbered counterparts, within +/- 10%. Some people prefer to collect PC copies because it's a little easier to get a matching set of "PC" books then a matching set of a specific numbered book. However many others would prefer a number, especially a low number.