This proposal is known as "Multiple First Past the Post" using multi-member electorates.
This was the system used for the Australian Senate many years back.
The disadvantage (and principal reason it was changed over here) is because it typically produces large swings and very skewed results.
I'll explain by way of example:
In California, Kerry and the Dems carried the state with 54.31% of the vote. Assuming a similar result in the Congressional race, you'd have 54.31% of the population casting their 53 votes for the entire 53 candidates put up by the Dems. Enough to elect all of the positions.
New Hampshire is a good example of the large swings - in 2000, Bush carried the state. If voters voted the same way for the Congressional race, there would be two Republicans, who just managed to get elected. In 2004, the state swung to the Dems and it would have completely changed over. Ohio would probably be an even better example if it flips in 2008.
If I was suggesting changes, I'd put forward a couple of ideas:
Preferential voting: allowing voters to allocate preferences assists minor parties. If people vote for a minor party presently, they realise their candidate probably won't be elected and it prevents them from voting for a major party candidate (which may influence a close race) resulting in their least-preferred candidate winning. Allocating preferences would at least allow them to vote in order of preference.
For President, I most prefer the Nebraska/Maine model of CD+2.
I like the idea of Congressional Districts because it means that Members of Congress can focus on their individual regions.
Maybe I wasn't clear when I typed this. What I propose is totally different than the old Australian multiple-FPTP system because, let's consider California's example, I propose that a voter gets a number of votes equal to the number of U.S. House seats his state gets. In this case, a Californian voter would have 53 votes but could vote for more than 1 candidate in his Congressional District race.
