Ask the commenters in this thread: What webapps decrease your productivity? Preferably those we haven't yet heard of? I imagine the answers could turn out much more interesting :-)
Youtube. I have to type in the track I am searching for. I would like some sort of Voxli hack for Youtube that will allow speech input (Hold Y + Say the name of the video you are looking for/or say Repeat).
StumbleUpon.
Faecbook, as well, but not so much. There's not as much to do on there. StumbleUpon is a potentially infinite time sink.
In fact, I'd say Google Reader has increased my productivity, since once I've skimmed the days articles from Slashdot/TechCrunch/etc, I crack on with some work, and I'm not as tempted to use SU.
