Been using this on one of my websites for a while now and the members love it. I think I'm a bit sidebar heavy at the moment, this could stand out better (my bad not the plugins) and yet it still gets used more than 'similar threads' and other similar sidebar-able add-ons.
Once I've complete the porting of all my forums from VB to XF, and have ensured no old URL's are in search engine indexes, I'll have only the Trending Topics in the sidebar, and I'm sure it's one of those add-ons that'd be heavily missed by members if I ever removed it!
Yet the 'related threads' etc sure wont.
Well done Stuart and Daniel. :) Keep up the good work.