The fact that the format is read/filtername rather than read?filter=filtername or anything else should probably go in a FAQ eventually.

On the navbar, where it has "Filter: All Subscriptions, Journals Only, Communities Only, Syndicated Feeds" in a drop-down, it might be good to add the filters into that drop-down - that was where I looked for it first when I was trying to figure out how to apply a filter to my reading page.