Some folks love the art in their PDF game books, others just don't care. For some publishers its a high priority, other's are happy to use clipart.
Here's where I fall in the scheme of things as a customer:
1 - The Cover is Where it's At - Since you can't flip thru a PDF like you might a book at the bookstore, your cover is the first impression. Sometimes, its the only impression. Make it count.
2 - Don't go Crazy on the Pages - Some publisher's like to make the page around, behind, below their text all supped up with background art and such- DON'T! It can cause issues with certain e-readers (the Amazon Kindle / Kindle DX comes to mind, but it messes with others too). It wastes my ink if I want to print out the pages. Last, it can make some products a real pain to read. This last part applies to print books too.
3 - Less is More - Remember, if I decide to print your product out, the art is going to kill my ink. Black and white art is fine. Less shading and filling is better. Heck, if you can give me two versions (one for printing, one for on screen reading) so much the better.
4 - No Art is Better Then Crap - If you aren't an artist, don't know one, can't afford one, use some of the great clipart that is available. Or avoid the art altogether. Trust me, no one wants to see bad art in an otherwise good product.
5 - Don't Forget the Tablets - As iPads and other tablets take off, more and more RPG PDFs (and other e-reader formats) are going to be read on electronic devices. White Haired Man and Greg (He of Boundless Creativity) are already taking that into account, and I expect others to soon follow suit.
Just some of my thoughts.
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