In the UK we limit the number of elections that can be held on the same day. The last three General Elections have coincided with County Council Elections - and there are some who still argue that two elections (possibly three if there is a district council by-election) is too much for the poor voter to cope with.
In the US Election Day can cover a whole host of elections - from the Presidency to the local dogcatcher. On November 4th US citizens will have a number of federal; state and local positions to vote on (and some will have votes on issues).
Over the period from now until Election Day I will post entries on some of the key Congressional races. A few points to note. In the US the incumbancy factor is greater than in the UK. Being a Senator or Congressman gives one greater name recognition; and more opportunities to raise campaign funds (who'll invest more in a challenger - when the incumbent has power to affect Government spending - British MPs may weep at this point!!!)). As a result "Open" seats are the more competitive. Americans are also more prepared to cross-vote - voting for a Democratic Congressman but a Republican for President. In fact some people take the American view of balanced powers so seriously that they deliberately cross vote.
