I have wondered about how Kobo has come up with some of their recommendations - and I suspect it is based on erroneous tags/descriptions provided by publishers.
But, in filtering the recommendations, I have found books I am interested in and wouldn't have found otherwise. I have found that:
About 30% are books that I am not interested in and can't understand why Kobo is making the recommendation,
About 40% are recommendations that I can understand but am not interested in (read the biography of one rock star and you end up having all of them recommended), and
About 30% are good recommendations of which about 25% (7.5% of total) are books I would not have seen otherwise.
Because of the books I would not have otherwise noticed, I am happy enough with the recommendations.
One thing that I do notice is that the recommendation engine appears to consider downloaded previews. So, if you download a preview, but don't like it, Kobo still appears to count it as something you are interested in.
Kobo, feel free to correct any of the assumptions I have made.