[AndrewP]

Just to add to the dry heave quotient, maybe rather than a time quota, but a delay in when you can request again depending on accumulated length of requests over the past, I dunno, week? In fact, you could add that track length to the - what is it? - initial hour waiting time. And subtract a minute for every hour since the request was made, down to a minimum of one hour.
Are we all gagging now? :-)

That way, the odd long track can come in, but will result in that person not being able to request another for a while.

Agree with Rick a bit. Having a restriction on what tracks can be requested makes one wonder why have the tracks in the library in the first place?