from ETF’s link above: “Naming her as running mate would mobilise the Republican base for McCain more quickly than if the angels Barry Goldwater, Ronald Reagan and William F. Buckley descended from heaven to anoint the Arizona senator live on C-SPAN.”
Personally, I’d like to see polling data to support that claim. For one thing who watches C-SPAN? 
Seriously, if the Republican base is going to mobilize for McCain they will find many reasons to do so, whether it’s Richardson, or Sebelius or anyone else in the VP slot. Clinton as VP might give them something extra to yap about but it will be very old news–and it could be potentially offset by the kind of voters that like both McCain and Hillary. Hillary is by now (rightly or wrongly) perceived as a centrist as against Obama’s liberal–there are inaccuracies here but my point is perception not reality. The Republicans will attempt to mobilize their base by portraying Obama as a foreigner: someone who is not quite American enough, not quite Christian enough, not quite hawkish enough, (not to mention the not so subtle racializing that will figure in all of this). In comparison to what I suspect they will do with Obama’s “otherness” I think that the old Clintonian claims, levelled at the VP on the ticket, might well be little more than a distraction. Does anyone really think that Clinton-hatred among Republican die-hards will do more for that kind of voter’s feelings toward McCain than Reverend Wright clips 24/7?
While I’m at this I find it rather odd how much vintage Republican paranoia about the Clintons has surfaced on these boards, including this thread. I was never a big fan of the Clintons when Bill was in office and am not a wild enthusiast about Hillary right now. That said, it’s one thing to talk about their Beltway politics, their manipulations and so forth. It’s another to speculate that they might be able to arrange an assassination or would actually do so. That kind of nonsense comes directly out of the Republican playbook and I think it’s time for Obama supporters to think twice about indulging that rhetoric.
For all his many flaws, Bill Clinton’s presidency was a popular one and America’s international standing under his leadership was way higher than it is now. Although many of his policies hurt the poor and although he was often not a team player, overall Bill’s record was one that Obama supporters could at the very least as having its ups and downs.
Whatever happens with Hillary’s future–again, I’m not certain that she’d be the most strategic choice for VP and I understand why some would see that choice as defeating Obama’s promise of change–I think that a chill pill about Hillary specifically and the Clinton presidency in general is in order.
IMO what Democrats need to be thinking about is not what will mobilize the Republican base but what will mobilize Democrats. Obama is a god-given candidate for bringing in voters who in the past have felt too young, too jaded, too disenfranchised. But Hillary represents another kind of Democrat and while I don’t believe that too many of the latter would ultimately stay home or vote for McCain I do think some kind of unity between HRC and Obama is crucial right now–and what’s more he seems to realize it too.