A) Missing artwork - I usually just type the album name into Google, save the image to my desktop and then select the tracks that are missing their covers and put them in manually. Takes less than a minute per album.
B) I've had that a few times - if you have access to another computer, try the disc in that - I've found a lot of discs that won't rip on my laptop, but do it no bother on my wife's or on my work PC.