Here is my take. First, it is entirely appropriate for presidential candidates to be thinking about and planning their transition at this point. In fact, both candidates should have been doing this months ago (see the White House Transition Project on this important topic). Barack Obama has been; John McCain started later, perhaps too late. Second, it would not be unprecedented for a presidential candidate to ask someone to serve as chief of staff before Election Day. George W. Bush did this with Andy Card and it helped the transition immensely. Third, the president-elect would be well-served picking someone with Washington and White House experience. The last 4 chiefs: Erskine Bowles, John Podesta, Andy Card, and Josh Bolten all served in the White House previously as deputy chief of staff before being elevated to chief--a huge advantage for a prospective chief.
Rahm Emanuel and former Senator Majority Leader Tom Daschle (D-SD) have been named as potential chiefs. Emanuel makes a lot of sense--he worked previously at the highest levels of the Clinton White House and would be very familiar with the job and navigating the Beltway. His Congressional connections and credentials help. There are a few reasons why I think he would be reluctant to serve as chief: 1) he has 3 small children and his family lives in Chicago. The chief of staff job is the most time-consuming staff job in the White House--he would rarely see his wife and children. 2) He reportedly has aspirations to be Speaker of the House. He is high-up in the House leadership and has a trajectory which would likely result in him being Speaker in a decade or so should he remain in the House and Democrats maintain control. Becoming chief disrupts this trajectory. 3) He may be appointed to replace Obama in the Senate.
One reason why Obama might be reluctant to pick Emanuel: he has a very strong personality. The most effective chiefs get the most out of their subordinates because of the immense respect they command (e.g., Bolten, Card, Podesta, Leon Panetta); some of the weakest chiefs rule by fear and end up poisoning the well, so-to-speak (e.g., Don Regan, H.R. Haldeman). I'm not inferring Emanuel would morph into Haldeman or Regan, just that his personality could overpower and intimidate those in the lower rungs of the White House. However, a positive aspect of his forceful personality would likely be a disciplined White House staff. His immense political skill would also be a plus in the chief's role. Perhaps reprising his position from the Clinton White House as a senior adviser or counselor to the president, ala Karl Rove or Dan Bartlett, might make more sense.
Although I think Daschle will be a part of an Obama administration, I see him in a different role than chief--one his more laid-back personality and quiet demeanor is more suited to: perhaps OMB Director or Secretary of Agriculture.
Here's a pick for chief of staff I have yet to see speculated about much: John Podesta. Not only was he very successful as Clinton's last chief--surviving the Clinton impeachment crisis and keeping the White House staff from imploding--he's running Obama's transition team. Who better to make chief than a former chief himself who is functioning in the top transition post already? I wouldn't be surprised if this was already a done deal. If Podesta were to be the chief, his role as transition director allows him to hand pick his White House staff and hit the ground running as soon as the feet hit the pavement.