All of these posts are correct, and offer good insight into both the working & the limitations of photostream
The ways to avoid 'bad' photos ending up in the stream will all work, but they are quite an ineffecient way to do things.
You really have 2 options now
1) Just put up with bad, blurry photos in your stream & move on with life
2) Turn photo stream OFF most of the time, & turn it on only when you really want to show off some photos.
Until Apple allows the ability to indivudually delete photos from the stream, there's nothing else you can do.
Also, was just thinking. If you turn Photosteam off & delete its contents, THEN turn it back on again, will it fill the stream up with the last 30 days of photos currently on your camera roll? Or will it only add photos to the stream when you start taking new photos on your iphone camera?