In order to determine the length of the mp3, the player has to actually open the file and then close it. The Zune software interferes with the player opening the file after upload, and as such you have to unplug the phone from the computer after uploading before closing the "I'm done" pop up box. I'm guessing that the 0-length issue might have been due to that. Try deleting that book and re-loading it to the phone, making sure to unplug the phone before continuing (or, alternatively, using the SDK's WPConnect.exe which doesn't interfere with the media being opened).
It might be useful to add a "determine durations" type button on the load screen that would let you try to determine them again at a later time instead of re-loading them. What do you think?
30 second skip could definitely be useful. I'll see if I can find a good way to incorporate it in the next update.
I really want fast play as well. Unfortunately the MediaElement player I have to use to be able to set positions doesn't support it. I'll definitely be watching the updates as they come out for supporting that.
I'm dreadful at UI stuff, but I have a friend who I can probably rope into giving it some love.
Play under lock and the configureable port are in the next update, which I will finish testing and submit tonight...