The Democrats stand a good chance of getting a pretty much filibuster-proof majority in the Senate or at least a strong enough majority that it would take all the Republicans (including Joe Lieberman) to block the Dems' proposed bills from coming to a vote.   If that happens, "working across the aisles" to the extent of compromising core principles may not be needed.

Plus, Obama has a record of working with Republicans successfully in both the Illinois legislature and the US Senate.   That's part of why so many idealistic progressives are becoming disenchanted with him to varying degrees. He's seen as more of a centrist and too much a corporatist for the more liberal Democrats to be wildly excited about his candidacy.
But if he were a Dennis Kucinich type Democrat, the corporatist "mainstream media" would destroy his chances of winning against the "experienced" avuncular "war hero and maverick" McCain.   

As it is, little is being accomplished in Congress now, because the Democrats hold only a rather small majority in the House (with quite a few Dems being "blue dog" Democrats and the party as a whole being like cats who resist being "herded") and because the Republicans in the Senate in this past year have filibustered more bills than any Senate since the inception of this company. The network and cable news channels don't report that, though; they usually present it as "such and such bill failed to pass" or "the Democrats could not garner enough votes to pass such and such bill," even when in reality the bill had enough BI-partisan support to easily pass if it had been brought to the floor for a vote. Very little will ever be accomplished in the US Senate if the minority political party insists on filibustering every bill the party bigwigs don't support.

And, of course, George W Bush has been vetoing even a lot of bills that have bipartisan support. His claim to be one who "works across the aisle" has not been borne out any time since he became President. I fully expect Obama to be more so inclined -- even in cases where I'll probably wish he were not.