Obama has opened up a 10 point lead over McCain O(47%, M-37%) and a whopping 26 point lead over Clinton (O-59%,C-33%).

From WaPo:

WASHINGTON (Reuters) - Democrat Barack Obama has opened an 8-point national lead on Republican John McCain
as the U.S. presidential rivals turn their focus to a general election
race, according to a Reuters/Zogby poll released on Wednesday.

Obama, who was tied with McCain in a hypothetical head-to-head
matchup last month, moved to a 48 percent to 40 percent lead over the
Arizona senator in May as he took command of his grueling Democratic
presidential duel with rival Hillary Clinton.

[snip]


The poll also found Obama expanded his lead over Clinton in the
Democratic race to 26 percentage points, doubling his advantage from
mid-April as Democrats begin to coalesce around Obama and prepare for
the general election battle with McCain.

The attacks on him from Bush & then McCain, have backfired.

But Zogby said the attacks on Obama by Bush and McCain, who have been
critical of his willingness to talk to leaders of countries like Iran,
did not appear to hurt Obama. If anything, he said, it reminded voters
of McCain's ties to Bush, whose approval rating is still mired at
record lows.

"The president is so unpopular. To inject himself into a
presidential campaign does not help John McCain, particularly when
McCain is tied to Bush," Zogby said.