Perhaps a friend slot *lock* can be an option? Seems to me that giving a friend a single chunk isn't really doing much for them, whereas giving them priority for the entire time they are on the queue for that file would help them get it faster, or maybe some sort of timer or data limit or other reset trigger?
I find this very helpfull when you want to release a file and when you are the only source available on the network. With a friend slot lock (whatever your friend downlod from you, what file or even if he disconnect/reconnect), i could give a full file to a friend very fast and then it would be easier for other people having interrest in this file to find it and get it with 2 valid sources. Seeing a file with parts non-available (well, seeing , i mean for the 1.x users

makes a lot of people stop downloading it.
What's your idea about this ?