Executives of Web 2.0 companies and some members of Congress are pressing for a reversal of the Pentagon’s decision to block access to several popular Web sites on military networks. The decision, abruptly made this week, cuts off troops’ access to such sites as YouTube, MySpace, Metacafe, IFilm, StupidVideos, FileCabi, BlackPlanet, Hi5, Pandora, MTV, 1.fm,…