Hillary's greatest weakness in the general election is that she has almost no cross over appeal. She is deeply despised by almost all Republicans and has considerably less support among independents than Sen. McCain or Sen. Obama. Although she has poled better than Obama among white male Democrats - as a demographic she is generally disliked by independent white male working class voters and all the more so in the South, the West and in small town and mid size cities. The fact that she has scored well in West Virginia and other such primaries was in contrast to Sen. Obama in a Democratic primary - This would be quite different that in contrast to Sen. McCain in a general election.
In order to win the Democrats have to have a ticket that can carry at least some states from either the West, the South or Southern border states. Although it is a given that McCain and the Republicans will win most of rural America and most white males votes -- in order to win - the Democrats have to make a respectable showing in rural America and among white males. I cannot see how Hillary on the ticket would strengthen the ticket in either the West or the South (including border states) or strengthen the ticket among white males and or help make a respectable showing in small town and mid size city America. Obama's weakest points in a general election is in Southern and border states and among white males and in small towns/mid size cities, outer suburbs and rural areas.
In the state by state counting that Obama would need in order to win a general election this would play out very differently than exclusive Democratic Party caucuses and primaries in places like Wyoming or North Carolina; or West Virginian for that matter. For Sen. Obama to win, I cannot see how he can do it without broadening his appeal in these areas. And I do not see how Hillary would be anything but a hindrance. So from my point of view, the V.P. candidate needs to be a populist Southerner or Westerner or border stater who appeals to white males and who would have appeal in small towns, outer suburbs, rural areas and mid size cities.
This is where the weakness lies with the Democratic Party whether it is in the South, the North, the East or the West. Even in a fairly Democratic state like Pennsylvania or New York, the city areas and immediate suburbs tend to go strongly Democratic with the outer suburbs, small towns and cites and rural areas going strongly Republican.
http://www.usatoday.com/news/politicselections/vote2004/countymap.htm