I originally meant to post this on July 4th, then got distracted for a few days! Today is the 4th of July, and the national holiday for our brethren to the south. I think that the USA has a great system, with nice checks and balances between the executive, judicial and legislative branches. Off the top of my head, there is only one thing that I would reconsider about the US system, and that is the electoral college.
I understand how and why it was introduced, but to me it seems an unfortunate relic of a bygone era. Modern American voters are not a mob, and (while some may disagree!), they do not need an electoral college to choose the 'right' candidate in case the voters attempt to elect the 'wrong' candidate. Further, the idea that regional voices should be counted differently, and that a voter in Wyoming has greater worth than a voter in California, should be a bit insulting.
Simply counting one vote as one vote, all votes equal, and then one of the quirks of US Presidential elections will disappear - the pursuit of 'swing states'. All votes will count, and a New York Republican vote will be as valuable as a Texas Republican, and a Montana Democrat's vote will have meaning. An election will not depend on hanging chads in Florida, and candidates will be able to focus on matters of interest to the nation, and not to special interests in a scattering of regions.
Of course, it may lead to interesting results when a third party gets to be a voice in the election - but that's all part of the fun with elections. And overall, I think we have far more things to fix here in Canada with our unelected senate and near-absolute power in the PMO.