This is pretty much perfect! To the point where it works for some things slightly outside its intended usecase - eg, its fantastic for blocking all the irrelevant pintrest results which I never want to see - but, also, for example;
When searching javascript (and sometimes php) documentation, w3schools is always the top few results, and I find it pretty useless, especially compared with the lovely, developer.mozilla.org docs.
So, I block w3schools, and, if I don't get the results I want from a more useful source, then uBlackList suffixes 'About 11 results' with 'uBlacklist has blocked 4 sites "Show"', which restores them in-place, so I keep access to the low value results.

One very minor thing I had to get used to was that the "block this site" link is where the "cached" link used to be, and in the same coloured text.
But, thats Google's fault for moving the "cached" link, and theres no more sensible place to put the "block this site".
(Adding it to the dropdown containing 'cached' would be worse, since, "cached" isn't available for every result, and, the presence of the dropdown arrow is how I know)