Sanford Levinson makes the case that the celebrated US constitution is actually totally whack. I tend to agree. For a lengthier exposition of Levinson's views, see Cass Sunstein's review of his new book which lays out the argument in some detail. Sunstein is pretty dubious, but I find his counterarguments unpersuasive, except on the point that Levinson's calls for a "do-over" just seem utterly unrealistic.
Let me try, however, to locate a more policy-relevant point here. The United States semi-frequently finds itself in the business of trying to assist other countries in making transitions to democracy. Thanks to our country's habit of Founder-worship, there's a tendency to push American-ish political institutions on other nations. Empirical research (see George Tsebelis' Veto Players for a summary of much of it), however, indicates that US-style proliferation of veto points makes democratic consolidation much more difficult. In the American context, an extremely large number of veto points serves, in essence, to impede progressive social reform, which is unfortunate. In young democracies without entrenched norms, however, it tends to simply encourage people to break the frequent deadlocks through extra-legal means -- coups or paralyzing street violence. This has been a particular problem in Latin America where the US influence has been at its highest.