Earlier today, venture capitalist Fred Wilson of Union Square Ventures wrote a post expressing concern that Web startups tend to languish after they are bought by big companies. To help make his point, Wilson reproduced the comScore chart above, which suggests that the number of people visiting the bookmarking service del.icio.us, which is owned by Yahoo, has dropped off considerably over the past nine months. Wilson was an investor in del.icio.us and profited from its sale to Yahoo in December, 2005. Yet he still laments its apparent struggles under Yahoo’s ownership.