Update: It appears that the upper limit has simply been changed to 1000.
Unless my eyes are playing tricks on me, it seems Google Reader is finally displaying the actual unread item count next to feeds and folders, instead of defaulting to the arbitrary "100+" indicator. I was flipping back and forth between tabs a few minutes ago when my mind's eye happened to register the >100 item counts.
In the [mostly positive] Google Reader piece I put up a few weeks ago, I said the following: "‘100+' is meaningless. This probably burns me up more than anything else. How hard is it to say 43423 unread items? Hint: it's not hard at all." Mission accomplished.