Agreed, streaming algorithms and sketches are a fascinating topic. The article's author, Graham Cormode, has been conducting research in that area for a long time and is one of the co-authors of the Count-Min Sketch paper.

Basically a Count-Min Sketch is the same thing as an undersized counting Bloom filter, but it's used quite differently. This allows for loads of interesting operations. First, there's the estimated number of occurrences of an element (how often has it been added?), but it can do more complex things as well, such as quantiles and heavy hitters.