I know I'm behind the times a bit, but it started with the "currently listening to" interest (that I still have yet to implement) but then when I saw this link, I thought I'd mention it, since it's the next logical step.
Looks like you can set up a "currently reading" link (that can even get associated with an Amazon associate id).
[found via Purple Goddess]
(FYI – if you have an alternate way of doing this, I'd be interested in hearing about it… just for curiosity sake)